SummaryPlasma concentrations of chlorpromazine (CPZ) and six metabolites were measured in 12 chronic schizophrenic patients on a fixed dose of CPZ. All six metabolites were measured in significant concentrations, ranging from 12 to 57% of the parent drug concentration. They are listed in order of decreasing mean concentration as follows: chlorpromazine-N-oxide > chlorpromazine sulfoxide > 7-OH chlorpromazine > Nor2chlorpromazine sulfoxide > Nor2chlorpromazine > Nor1chlorpromazine. CPZ concentrations showed significant correlation with the 7-OH chlorpromazine metabolite concentration. Since these metabolites have been associated with in vitro activity and occur in significant concentrations, it is recommended that all six metabolites be measured in studies correlating drug levels with pharmacodynamic effects.