A pharmacokinetic study was done on 10 depressed patients (DSM-III-R 296.3). The patients were treated with Sintamil (R) (nitroxazepine HCl) with titrated dose from 75 mg to 225 mg for 6 weeks. Plasma levels of nitroxazepine (Sintamil (R)) and its metabolites desmethyl (D), N-oxide (N-O) and carboxylic acid (c) were estimated. Anti-depressant efficacy was judged by reduction in Hamilton Rating Depression Scale (HDRS) scores, and tolerability was monitored by reports of unwanted effects.The overall reduction in HDRS score was about 50% by 6 weeks. The plasma levels of nitroxazepin (ng/ral) showed a rise from a mean ( +SEM) level. 47.0 4-7.3 on day 1 (dose 75 mg) to 129.84-24.6 on day 7 (dose 150 mg) (p< 0.01) and remained steady till day 21. There were large interindividual variations. The metabolites followed a similar pattern. The HDRS score showed a steady reduction between day 14 and 42 when the levels of nitroxizepine and des-methyl metabolites were maintained between 176.5 ng/ml to 251 ng/ml.