An intensive screening programme for potential diabetics in pregnancy was conducted in the University Department of Obstetrics and Gynaecology, Kandang Kerbau Hospital, Singapore, from June 1978 to December 1980. All patients with one or more risk factors for potential diabetes underwent an oral glucose tolerance tests (OGTT) with 50 g glucose loads. An abnormal OGTT was defined as one in which the second hour venous plasma glucose value was 7.8 mmol/1 (140 mg%) or more. In a group of 789 Chinese patients aged between 20 and 40 years, the overall detection rate of abnormal OGTTs was 15.5%. A significantly high proportion of abnormal OGTTs was found in patients with a direct family history of diabetes associated with random glycosuria during pregnancy and those with a previous history of 2 or more consecutive spontaneous abortions. However, in view of the relatively low detection rate of abnormal OGTTs in pregnant potential diabetics, a preliminary blood screening test would be useful to select those patients who require full OGTTs.