The steady state bioavailability and pharmacokinetics of propranolol over two consecutive dosing intervals were investigated in 18 black and 10 white normal volunteers following the administration of 20 mg of a test and reference oral dosage form, respectively, every 6 h. There were no differences (p greater than 0.05) between dosage forms in the mean (n = 28) area under the plasma concentration-time curve (AUC), maximum plasma concentration (Cmax) or time to Cmax (tmax) for propranolol or its active metabolite, 4-hydroxypropranolol. However, as a group blacks had lower plasma concentrations of propranolol during the second dosing interval (AUC-2 and Cmax-2, respectively) were significantly (p less than 0.05) lower in blacks, but there were no ethnic differences (p greater than 0.05) in tmax. The mean AUC and Cmax for the 4-hydroxylated metabolite during both dosing intervals were significantly (p less than 0.05) lower in blacks. Mean oral clearances of propranolol, assuming complete absorption, (range: 42.1-54.5 ml min-1 kg-1) were similar (p greater than 0.05) in each racial group. There were no substantial changes in heart rate or blood pressure in blacks or whites following propranolol administration. These data suggest that for oral propranolol, blacks have different absorption and disposition characteristics than whites.