The absorption, distribution and elimination of 14C- and 3H-azidomorphine, 3H-14-OH-azidomorphine, 14C- and 3H-azidocodeine and 3H-azidoethylmorphine were studied in comparison to 14-C-morphine. Whole body autoradiography of pregnant mice, quantitative estimations of tissue radioactivity in male mice, brain autoradiography, subcellular distribution in rat brain and elimination studies in rats were performed. Azidomorphine and morphine are absorbed from the gastrointestinal tract at the same rate but the absorption of 14-OH-azidomorphine, azidocodeine and azidoethylmorphine exceeds that of the formers. The azidomorphines pass across the blood-brain barrier more readily than does morphine. In rats treated with azidomorphines, 30--50% of the doses given were excreted with the urine the first 4 hours and about 90% within 48 hours; whereas 2--5% were recovered from the collected stools.