The efficacy and safety of the HMG CoA reductase inhibitor fluvastatin have been evaluated in a double blind study in 52 patients with familial hypercholesterolaemia. A standard AHA Phase II lipid lowering diet was prescribed throughout the study. After 6 weeks of a single blind dosage stabilisation period, in which patients received fluvastatin 40 mg qPM, patients were randomly allocated to one of two double blind treatment groups: group A (n = 24) received fluvastatin 20 mg b.d. for 12 weeks and fluvastatin 20 mg AM + 40 mg PM for an additional 12 weeks; Group B (n = 28) received fluvastatin 40 mg qPM during the entire study. Safety and tolerability were evaluated by the analysis of biochemical and haematological parameters, and ophthalmological and physical examinations. Efficacy was analysed by the determination of plasma lipids, lipoproteins and apoproteins. Fluvastatin 40 mg/d was associated with up to a 27.4% decrease in LDL-C and a 9.6% increase in HDL-C concentrations. Increasing the dose of fluvastatin from 20 mg b.d. to 60 mg per day in Group A was associated with a 7.1% decrease in LDL-C, a 12.1% increase of HDL-C and a 12.8% decrease in the LDL-C/HDL-C ratio. In comparison with Group B (40 mg qPM) LDL-C, HDL-C and the LDL-C/HDL-C ratio in Group A (60 mg) differed by -8.9%, 6.6% and -12%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)