Respiratory effects of 0.1 pM - .1 mM bombesin microinjected to the pre-Botzinger complex were studied in anaesthetised rats. Bombesin induced an increase in minute ventilation, respiratory frequency, a decrease in expiratory duration and shortening of inter-burst intervals on the EMG of diaphragm and external intercostal muscles. The responses to bombesin characterised by short latency, quick development (with the maximum in 3-minutes after microinjection) and found to be reversible. The effects of bombesin on membrane potential, input resistance and pattern of spontaneous activity ofpre-Botzinger neurons were investigated in brainstem slices. 1 nM bombesin introduced into the perfusion solution in most cases (68%) induced membrane depolarisation, an increase in input resistance and in spike activity of spontaneously active cells. The data obtained suggest that the respiratory effects ofbombesin at the level ofpre-Botzinger complex are caused by its action on the membrane of neurons.