A diabetic screening exercise involving 1627 subjects (1050 males and 577 females) was carried out in the Lagos Metropolis of Nigeria. Casual capillary blood glucose and/or urine glucose were tested for by means of dipsticks. The prevalence rates of undetected diabetes in the males and females were respectively 1.5% and 1.9%. Mean (+/- SD) casual blood glucose levels were higher in the females (82.8 (+/- 19.1) mg/100 ml) than in the males (75.9 (+/- 16.2) mg/100 ml). The prevalence of renal glycosuria was 1.3% in the males and 0.2% in the females. The prevalence of diabetes mellitus in the Lagos Metropolis appears high but similar to that in many other countries. The ambient blood glucose in the non-hospitalized subjects also seems to be not significantly different from values reported in other places.