Following administration of a single oral dose of 3 g probucol to healthy volunteers, mean peak plasma concentrations of 3.9 microgram/ml were observed at 24 hours. Successive blood levels measurements showed diphasic elimination, with half-lives of about 1 and 23 days. Plasma levels after a single 250 mg dose in volunteers are also reported. In 51 patients who received probucol 1 g daily for periods of 1 to 12 months, a concentration plateau was obtained within 1 to 3 months of treatment; the mean plasma levels ranged from 18.2 to 39.2 microgram/ml depending on the duration of probucol therapy. In another study carried out on 8 patients who were given the same daily dose during 12 months, the mean probucol plasma level at the end of that period was 18.9 microgram/ml. Repeated administration of probucol to healthy volunteers showed good correlation between dosage and blood levels.