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This report investigates the reasons for false negative cervical cytology in 94 out of 630 patients (15%) in whom cervical intraepithelial neoplasia (CIN) was diagnosed on colposcopically directed biopsy. Cervical smears were taken immediately before biopsy and the cases with false negative cytology were compared with those whose cytology was abnormal. Patients with false negative cytology were more likely to have been younger (P < 0.01), to have had fewer pregnancies (P < 0.001), to have had a less severe grade of dyskaryosis on their referral smear (P < 0.001), to have had no endocervical cells on the smear (P < 0.05), to have had a less severe grade of CIN on biopsy (P < 0.001), to have had no punctation visible at colposcopy (P < 0.01), and to have had no mosaic pattern seen at colposcopy (P < 0.05). We found no effect attributable to the patient's menstrual history, the interval between referral smear and colposcopy clinic visit, the smear taker or the type of spatula used to take the smear.

The estimation of the lecithin-sphingomyelin (L.S.) ratio on thin-layer chromatograms has been shown to vary depending upon the stain used to identify the phospholipids and the method employed to estimate the two components. The factors involved in causing these variations have been evaluated using standard phospholipid solutions and confirmed in clinical material. Staining with a phosphomolybdic acid stain followed by transmission densitometry was found to be an accurate and sensitive method for clinical purposes.

One hundred and ninety samples of amniotic fluid were analyzed for their surfactant content by measuring the lecithin-sphingomyelin ratio and performing the simple "shake test". The value of these tests in predicting the respiratory performance of the baby at delivery is discussed and the limitations of the tests is evaluated. It was concluded that the shake test is valuable only as a screening procedure for determining fetal lung maturity.~NTEREST has been expressed in estimation of the lecithin-sphingomyelin ratio (Gluck et al., 1971 ;Whitfield, 1972; and the total lecithin concentration (Bhagwanani et al., 1972a and b) of the amniotic fluid as a means of assessing fetal lung maturity and thereby predicting the likely respiratory performance at birth. These methods are involved and time-consuming and therefore attention has been directed towards simpler tests which would yield the same information. We have used both types of test and the results have been compared.

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