The presence of therapeutic drugs in the hair of psychiatric patients was investigated, and the method for simultaneous determination of antidepressant and antipsychotic drugs by GC/NPD and GC/MS was also established. Eight different psychotroic drugs were detected from the hair of 32 subjects, and chlorpromazine and clozapine concentrations in the hair were found to be dependent on the dosage and the correlation coefficients were 0.8047 (P < 0.001, n = 16) and 0.7097 (P < 0.001, n = 16) respectively. Segmental analysis demonstrated that there was a correlation between the subject's drug exposure history and the distribution of drug along the hair shaft.