OBJECTIVE - To determine the association between exercise-induced albuminuria and the development of microalbuminuria over 10 years in subjects with insulin-dependent diabetes mellitus (IDDM) who were initially normoalbuminuric.RESEARCH DESIGN AND METHODS - Thirty-two patients with IDDM and a resting urinary albumin/creatinine ratio (U-A/U-C) 4.3 mg/mmol (>30 mu g/min). Results were compared with resting U-A/U-C after a 10-year follow-up. Persistent microalbuminuria was defined as a U-A/U-C >2.1 mg/mmol (>15 mu g/min) in each of two early-morning urine collections.RESULTS - Five patients developed persistent microalbuminuria after 10 years, and four patients were predicted by a positive exercise test. Two patients with positive exercise tests did not develop persistent microalbuminuria. The sensitivity of the exercise test for the development of microalbuminuria was 80% (95% confidence interval [CI] 65.8-94.2%) and the specificity was 92.9% (95% CI 83.9-100%). The postexercise U-A/U-C was positively associated with the U-A/U-C after 10 years (P = 0.005, R(2) = 0.31). This association was independent of HbA(1), systolic blood pressure, body mass index, and duration of diabetes, but HbA(1) remained an independent predictor (P = 0.02) of U-A/U-C at follow-up.CONCLUSIONS - Exercise testing may be useful for identifying normoalbuminuric IDDM patients who are susceptible to the later development of microalbuminuria.