The present communication deals with an analysis and comparison of the principal physical measurements, physical characters and relative bodily proportions in groups of boys and girls at corresponding ages who were under treatment for asthma and rheumatism respectively in the special clinics established at the Sick Children's Hospital, Great Ormond Street, and of other groups of boys and girls of similar ages with no history of asthma or rheumatism and no obvious serious impairment of general health who were attending the Outdoor Department of the hospital for treatment of trivial ailments. The last-mentioned series of boys and girls have been assumed to represent the normal hospital population and have been referred to throughout as the normal groups. The object of the investigation was to determine if there was any real evidence that the asthmatic and rheumatic children differed from one another or from the normal children in general physical type or build. The inquiry has been restricted to children in the age period 6–12 years, and these have been taken in two-yearly age groups in order to provide more adequate numbers of observations for comparison. In all, the characters of approximately 1212 children have been dealt with. Of these, 368, 236 boys and 132 girls; 459, 189 boys and 270 girls; and 385, 195 boys and 190 girls, were considered to be asthmatic, rheumatic and normal respectively. A study of the frequency distributions, mean values and variabilities of the characters compared at the corresponding ages in the three groups of boys and girls seems to provide a reasonable basis for the following conclusions:1. The corresponding averages of practically all the absolute physical measurements brought under review are in such close agreement in the contrasted groups of asthmatic and rheumatic children that the data provide no evidence of any real difference in the general dimensions of children with the respective diseases. Though the average antero-posterior diameter of the chest is probably greater in the asthmatic than the rheumatic children, no emphasis can be laid on this feature as it may be, in part, the result of the disease.2. Though at some ages the mean dimensions of a few characters in the asthmatic and rheumatic groups do differ from the corresponding averages in the normal series, the differences are not sufficiently consistent at the different ages and in the two sexes to indicate any real divergence from the normal.3. A comparison of the relative proportions of the body as expressed by the percentage ratios or indices, stem length/stature, body length/stature, biacromial diameter/body length, bicristal diameter/biacromial diameter and length of arm/length of leg, at corresponding ages in the asthmatic and rheumatic children does not provide any definite evidence that children suffering from these two diseases differ from one another in morphological type.4. Though occasionally, at one or more ages, one or more of the indices used to express the relative proportions of the body may appear to differ in mean value from the normal averages at the corresponding ages the differences are not sufficiently consistent in regard to age and sex to suggest any real divergence from the normal.5. Comparison of the frequency distributions of hair colour shows that the asthmatic children do not really differ from the rheumatic children in respect of pigmentation. The rheumatic children do not differ from the normal, but both the asthmatic boys and girls show a relatively greater excess of the blonde haired type and a greater deficiency in the dark haired as compared with the normal than might be expected to occur as a chance variation.6. With regard to distribution of eye colour, the asthmatic boys do not differ from the rheumatic boys, but the asthmatic girls appear to have a relative defect in brown eyes and a relative excess in blue eyes as compared with the rheumatic group; neither in boys nor girls with asthma or rheumatism can the distribution of eye colour be said to differ significantly from the normal on the data available.7. There is no definite evidence that the proportions of relatively long and slender and short and thick-set types, as appraised by general inspection, amongst asthmatics differ from the normal.8. There is no evidence in the data for boys or girls that the distribution of grades of posture differs significantly in either the asthmatic or rheumatic groups from the normal, though in girls with rheumatism the habitual posture appears to be relatively worse than in those with asthma.9. Both in regard to form of face, as expressed by the upper and total facial indices, and form of head, as represented by the cephalic index, the groups of asthmatic and rheumatic children do not differ significantly from one another or from the normal.10. The differences in the three groups of children, the asthmatic, the rheumatic and the normal, in respect of the aggregate of physical characters brought under review are relatively so slight that they cannot be considered to support the view that asthmatic and rheumatic children really differ on the average from one another or from the general population of children from which they are drawn in bodily conformation or physical type, though they may possibly, indeed probably, differ in other constitutional traits.