The presence of islet cell antibodies (ICA), complement fixing islet cell antibodies (CF-ICA), other organ-specific autoantibodies, insulin antibodies and two different types of immune complexes (AgAb) in diabetic pregnant women treated with insulin during pregnancy was investigated and compared with maternal metabolic control and with the course and outcome of pregnancy. One hundred and eighteen pregnant diabetic women were grouped according to type of diabetes: 56 were insulin-dependent diabetic patients who had been previously treated with insulin (Group 1); 23 were non-insulin-dependent diabetic patients who had previously received diet or oral treatment (Group 2); 39 had gestational diabetes (Group 3). 94 patients were subjected to regular check-ups during pregnancy and blood samples were taken during the last month of pregnancy (phase A); some were treated with standard preparations of insulin, the remainder with purified insulins. 24 patients were treated with purified insulins (a bovine and porcine mixture) on entering the study and blood samples were taken at regular intervals during pregnancy (phase B). ICA were detected in 12% of the patients in Group 1 and in 5% of those in Group 3. There was no significant variation in the titre during the gestational period. ICA were not detected in the patients in Group 2. No CF-ICA were found in any of the patients. The positivity of the other organ-specific autoantibodies was similar to that the normal control group. Insulin antibodies were found in concentrations of 67%, 73% and 25% in Groups 1,2 and 3 respectively during the last month of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)