To determine whether there are relationships between nephropathy, retinopathy and putative risk factors at points very early in the development of long-term complications of IDDM, we have analyzed baseline data pertinent to nephropathy in the 726 subjects in the primary prevention cohort and the 715 subjects in the secondary intervention cohort of the DCCT. AER correlated positively with CCr and HbA1c in both cohorts and with degree of retinopathy and duration of IDDM in the secondary cohort. Within the secondary cohort only mean BP and HbA1c levels were significantly increased (P < 0.005) in the 73 subjects with AER > or = 28 micrograms/24 hr compared to the 642 subjects with AER < 28 micrograms/24 hr. Stratification of all subjects in the secondary cohort showed significant associations (P < 0.001) between retinopathy level, AER, duration of diabetes at entry and entry HbA1c. Even very early in the development of retinopathy and nephropathy, there is a relationship between them and with level of metabolic control. The prospective studies of the DCCT are designed to answer the question of whether intensive diabetes treatment will affect the development and/or progression of retinopathy, and, possibly, of nephropathy.