We compared the action of subdiaphragmatic vagotomy upon the anti-exploratory and motor depressant effects of caerulein, an agonist of cholecystokinin (CCK) receptors, in male rats. Vagotomized rats entered more frequently into the open arms of elevated plus-maze compared to intact control rats. Caerulein (1 microgram/kg subcutaneously (s.c.)) significantly suppressed the exploratory behaviour in vagotomized rats but not in intact and sham-operated rats. In contrast, subdiaphragmatic vagotomy did not change the locomotor activity of rats in open field compared to intact and sham-operated animals. At a higher dose (10 micrograms/kg s.c.), the caerulein pretreatment markedly decreased the number of line crossings, rearings and head-dippings of intact animals in open field. In sham-operated rats caerulein also suppressed the locomotor activity, whereas in vagotomized rats it only tended to reduce the frequency of rearings. Consequently, the present study revealed the different action of vagotomy upon the motor depressant and anti-exploratory effects of caerulein. These results support the view that CCKA receptors in the gastrointestinal tract are mediating the motor depressant, whereas CCKB receptors in the brainstem are involved into the mediation of anti-exploratory effect of caerulein.