The effect of simvastatin (10-20 mg/day) on kidney function, urinary albumin excretion rate and insulin sensitivity was evaluated in 18 Type 2 (non-insulin-dependent) diabetic patients with microalbuminuria and moderate hypercholesterolaemia (total cholesterol > or = 5.5 mmol.l-1). In a double-blind, randomized and placebo-controlled design treatment with simvastatin (n = 8) for 36 weeks significantly reduced total cholesterol (6.7 +/- 0.3 vs 5.1 mmol.l-1 (p < 0.01)), LDL-cholesterol (4.4 +/- 0.3 vs 2.9 +/- 0.2 mmol.l-1 (p < 0.01)) and apolipoprotein B (1.05 +/- 0.04 vs 0.77 +/- 0.02 mmol.l-1 (p < 0.01)) levels as compared to placebo (n = 10). Both glomerular filtration rate (mean +/- SEM) (simvastatin: 96.6 +/- 8.0 vs 96.0 +/- 5.7 ml.min-1 x 1.73 m-2, placebo: 97.1 +/- 6.7 vs 88.8 +/- 6.0 ml.min-1 x 1.73 m-2)(NS) and urinary albumin excretion rate (geometric mean x/divided by antilog SEM) (simvastatin: 18.4 x/divided by 1.3 vs 16.2 x/divided by 1.2 microgram.min-1, placebo 33.1 x/divided by 1.3 vs 42.7 x/divided by 1.3 micrograms.min-1)(NS) were unchanged during the study. A euglycaemic hyperinsulinaemic clamp was performed at baseline and after 18 weeks in seven simvastatin- and nine placebo-treated patients. Isotopically determined basal and insulin-stimulated glucose disposal was similarly reduced before and during therapy in both the simvastatin (2.0 +/- 0.1 vs 1.9 +/- 0.1 (NS) and 3.1 +/- 0.6 vs 3.1 +/- 0.7 mg.kg-1 x min-1 (NS)) and the placebo group (1.9 +/- 0.1 vs 1.8 +/- 0.1 (NS) and 4.1 +/- 0.6 vs 3.8 +/- 0.2 mg.kg-1 x min-1 (NS)).(ABSTRACT TRUNCATED AT 250 WORDS)