Cholesterol absorption and metabolism and LDL and HDL kinetics were investigated in 11 hypercholesterolaemic non-insulin-dependent diabetic men off and on a hypolipidaemic treatment with sitostanol ester, (3 g sitostanol daily) dissolved in rapeseed oil margarine, by a double-blind crossover study design. Serum total, VLDL and LDL cholesterol and apoprotein B fell significantly by 6 +/- 2, 12 +/- 6, 9 +/- 3 and 6 +/- 2%, mean +/- SEM, and HDL cholesterol was increased by 11 +/- 4% (p < 0.05) by sitostanol ester. LDL cholesterol and apoprotein B were significantly decreased in the dense (1.037-1.055 g/ml), but not light, LDL subfraction due to a significantly diminished transport rate for LDL apoprotein B, while the fractional catabolic rate was unchanged. HDL kinetics, measured with autologous apoprotein A I, was unaffected by sitostanol ester. Cholesterol absorption efficiency was markedly reduced from 25 +/- 2 to 9 +/- 2% (p < 0.001) during sitostanol ester followed by proportionately decreased serum plant sterol proportions. Cholesterol precursor sterol proportions in serum, fecal neutral sterol excretion, and cholesterol synthesis, cholesterol transport, and biliary secretion were all significantly increased by sitostanol ester. We conclude that the sitostanol ester-induced decrease in cholesterol absorption compensatorily stimulated cholesterol synthesis, had no effect on fractional catabolic rate, but decreased transport rate for LDL apoprotein B so that serum total, VLDL and LDL cholesterol levels were decreased.(ABSTRACT TRUNCATED AT 250 WORDS)