In order to determine the prevalence of glucose intolerance in pregnancy, 1267 consecutive women attending the antenatal clinic of the Aga Khan University Medical Centre were subjected to a 75 g glucose challenge followed 2 hr later by plasma glucose determination irrespective of gestation on the first antenatal visit. The test was repeated at 28-32 weeks of gestation if the patients had an abnormal initial screen at less than 28 weeks gestation and a normal glucose tolerance test on diagnostic follow-up and for those who had a risk factor for gestational diabetes and a normal initial screen at less than 28 weeks gestation. The glucose challenge test was abnormal (2 hr plasma glucose greater than 140 mg%) in 8.6% of the screened population. Follow-up oral glucose tolerance test on these patients revealed a prevalence of 3.2% of gestational diabetes and 1.9% of impaired glucose tolerance test based on the modified O\u27Sullivan criteria. Improvement in cost effectiveness of screening programmes was adjudged possible by avoiding glucose tolerance tests in patients with 2 hr plasma glucose value of greater than 170 mg% after a 75 g oral glucose challenge for screening