1. A g.l.c. method for quantitative determination of loxapine (2-chloro-11-(4-methyl-1-piperazinyl)dibenz(b,f)(1,4)oxazepine), in human plasma and urine is described. 2. Preliminary pharmacokinetic data on plasma concn of loxapine over 12 h from five psychiatric patients who received a total average dose of 80 mg of loxapine succinate per day orally for twelve weeks are presented. 3. In addition to unchanged loxapine, three urinary metabolic products, namely aromatic ring-hydroxy loxapine, desmethyl loxapine and loxapine-N-oxide, were identified using g.l.c.--mass spectrometry.