The relationship between seasonal asthma and sensitivity to the house-dust mite has been investigated in a country with large seasonal variations in relative humidity.Of seventy-eight African asthmatics, 641",, gave a history probably suggestive of sensitivity to house-dust, and 55-l"o a history strongly suggestive of such sensitivity. On skin testing. 35-9% had strong reactions to the house-dust mite Dermatophagoides pteronyssinus, compared with 19";, of fifty-one matched controls without symptoms of chest disease. Few had either a history or skin tests suggestive of pollen or mould sensitivity. Most of the asthmatics were worse during the hot. wet season when the humidity is highest. This is also the time when in-patient asthmatics are most numerous.D. pteronyssinus grows well in warm, damp conditions and it is suggested that sensitivity to this mite may play a significant role in the marked seasonal changes seen in our asthmatic patients.

The prevalence of asthma in a small African town has been assessed using two questionnaires. The first was put to 9768 subjects aged 5 years and older and the second, more detailed, questionnaire to random selections of these subjects grouped according to their replies. The overall prevalence of asthma was 1-40%. In those under 20 years of age it was 1-20% and in adults, 1-57%. This adult rate is similar to those in developed countries but that in children is lower. The relative paucity of childhood asthma is compatible with the suggestion that infestation with parasites may protect against the disease.