The relationship between renal hemodynamic abnormalities and renal kallikrein activity was studied in streptozocin-induced diabetic rats. Diabetic rats were either not treated with insulin and had plasma glucose levels greater than 400 mg/dl (severely hyperglycemic diabetic [SD]) or were treated with 1.5-1.75 U/day protamine zinc insulin and had glucose levels of 200-300 mg/dl (moderately hyperglycemic diabetic [MD]). In SD rats, kidney tissue level and excretion of active kallikrein were reduced after 3 wk compared with age-matched nondiabetic control rats (tissue, 11.7 +/- 1.9 vs. 20.5 +/- 1.8 ng/mg protein, P less than 0.005; urine, 126 +/- 12 vs. 179 +/- 10 micrograms/24 h, P less than 0.005). Despite increased kidney size, renal plasma flow (RPF) was reduced in SD rats (5.38 +/- 0.23 vs. 6.37 +/- 0.20 ml/min, P less than 0.05). Glomerular filtration rate (GFR) was not significantly lower (2.77 +/- 0.60 vs. 3.02 +/- 0.56 ml/min). In MD rats, kidney tissue level and excretion of active kallikrein were increased after 5 wk compared with age-matched nondiabetic control rats (tissue, 28.4 +/- 1.3 vs. 23.3 +/- 1.7 ng/mg protein, P less than 0.05; urine, 289 +/- 16 vs. 196 +/- 13 micrograms/24 h, P less than 0.001). In MD rats, GFR and RPF were increased (3.80 +/- 0.11 and 8.04 +/- 0.17 ml/min, respectively) compared with control rats (3.22 +/- 0.05 and 7.28 +/- 0.09 ml/min, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)