The purpose of this study was to investigate and compare the efficacy, safety, and patient acceptability of a new formulation of colestipol, colestipol tablets (T), with those of colestipol granules (G), in a randomized, double-blind, placebo-controlled, multicenter study. Three hundred and seventeen patients with primary hypercholesterolemia who were following a low-fat, low-cholesterol diet (NCEP Step I diet), and had low-density lipoprotein cholesterol (LDL-C) levels > or = 4.14 mmol/l (160 mg/dl) and < or = 6.46 mmol/l (250 mg/dl) were studied. Study medication was taken twice a day, with breakfast and supper, for 8 weeks. The six parallel treatment groups consisted of colestipol tablets 2 g b.i.d. and 8 g b.i.d., matching placebo tablets b.i.d., colestipol granules 2 g b.i.d. and 8 g b.i.d., and matching placebo granules b.i.d.. Study endpoints included absolute change and percentage change from baseline in selected lipid, lipoprotein, and apolipoprotein measurements; LDL-C lowering was the primary efficacy endpoint. Treatment with colestipol tablets and colestipol granules resulted in virtually identical, statistically significant (P < or = 0.05) reductions of LDL-C, total cholesterol (TC), TC/HDL-C, and apolipoprotein B (apo B). Compared with placebo, all active treatments (tablets 4 g/day, tablets 16 g/day, granules 4 g/day, granules 16 g/day) significantly reduced LDL-C (12%, 24%, 12%, 25%, respectively), TC (7%, 15%, 8%, 15%, respectively), TC/HDL-C (8%, 14%, 9%, 15%, respectively) and apo B (12%, 20%, 13%, 22%, respectively). All active treatments significantly increased lipoprotein particle AI (LpAI) (5%, 23%, 14%, 18%, respectively). VLDL-C and triglycerides increased significantly in the high-dose groups. The proportions of patients reporting adverse events, largely gastrointestinal-related, were not different among the active treatment groups. The treatments were well-tolerated, and no drug-related serious adverse events were reported. Patients experienced with granule medication prior to this study preferred tablets over granules. This study demonstrates that colestipol tablets are an effective treatment to reduce LDL-C in patients with primary hypercholesterolemia, are equivalent to colestipol granules, are well-tolerated, and are preferred over granules by patients.