In experiments on mice 3H-spiperone binding after intraperitoneal injection was studied. The binding of 3H-spiperone was saturable in the frontal cortex and subcortical structures, whereas in the cerebellum, the amount of radioactivity increased in a linear manner and was referred to as nonspecific binding. The neuroleptics haloperidol, chlorpromazine and sulpiride given 0.5 h before 3H-spiperone displaced 3H-spiperone in the subcortical structures in a dose-related manner. Although the level of the specific 3H-spiperone binding after intraperitoneal injection was lower than after intravenous injection, the intraperitoneal method is simpler, well reproduced and given results comparable with the intravenous method.