The kinetic characteristics of penicillamine are reported in four fasting subjects after four oral doses each. On late test days, tow of the subjects received an additional single dose 30 min after a large breakfast. On subject originally included in the study had to drop out because of gastrointestinal disturbances following each of two single doses of penicillamine. The fasting plasma levels of penicillamine observed in this study displayed an unusual double peak in the plasma levels after single doses. Individual subjects had consistent plasma level patterns for each of the four single doses but there was marked intersubject variability in patterns and kinetic parameters. The half-life of unchanged penicillamine ranged from 1.66 to 3.15 hr and the apparent plasma clearance ranged from 530 to 2300 ml/min. The administration of penicillamine following a large breakfast caused a reduction in the area under the penicillamine plasma concentration-time curve corresponding to a decrease in the extent of absorption of unchanged penicillamine.