Protein intake in relation to glomerular filtration rate (GFR) and urinary albumin excretion (UAE) has been studied in 96 insulin-treated diabetic patients, 20-40 years of age and without nephropathy. They had diastolic blood pressure (DBP) not exceeding 90 mmHg and a GFR exceeding -2 SD of the age-related value. They were without medications except for insulin. There were no significant differences in protein intake between diabetic patients with and without hyperfiltration (1.18 +/- 0.26 g/kg/d vs 1.21 +/- 0.42 g/kg/d, p = 0.75) or between diabetic patients with or without increased UAE (1.16 +/- 0.41 g/kg/d vs 1.24 +/- 0.37 g/kg/d, p = 0.37). No relations were found between protein intake and GFR or UAE in the whole sample, but a positive relation was found between UAE and protein intake in patients with increased UAE. Protein intake correlated with UAE in hyperfiltrators who use tobacco (n = 8, r = 0.85, p = 0.01), but not in non-users (n = 11, r = 0.24, p = 0.48). In conclusion our findings give no support for a relation between high protein intake and glomerular hyperfiltration in insulin-treated-diabetic patients. However, in contrast to non-users of tobacco, a positive relation was found between UAE and protein intake in tobacco users with hyperfiltration.