Pharmacokinetics and clinical effects of muzolimine were investigated in 6 hypertensive patients with incipient renal insufficiency. Muzolimine plasma levels were determined after the first dose and after 8 weeks of treatment with muzolimine (20 mg o.d.). The area under the curve of muzolimine plasma levels was greater after 8 weeks than after the first dose. Also, peak plasma concentrations were higher after 8 weeks; however, muzolimine half-lives in the beta-phase were unchanged. Blood pressure and body weight decreased with time. Muzolimine was well tolerated.