BACKGROUND The presence of sphincter of Oddi (SO) slow waves has been noted in earlier studies on the effect of cholecystokinin (CCK) on the SO, but a more thorough description of changes in SO slow-wave and pressure activity induced by CCK is needed. METHODS The SO and duodenum in anaesthetized rabbits were prepared with perfused catheters and bipolar electrodes. Increasing, successive doses of CCK (1/32 to 1/1 Ivy Dog Units (IDU)/kg) were administered intravenously every 15th min. The digitized recordings were scored on a computer in control and stimulatory CCK sequences. RESULTS CCK had a significantly stimulatory effect on SO and duodenum when estimated as area below pressure peaks (p < 0.001), but quantitatively, this effect did not differ in the two organs (p = 0.59). CCK significantly decreased SO slow-wave frequency (p < 0.05), whereas a similar trend in duodenal slow-wave frequency failed to reach statistical significance. Most pressure peaks recorded from the SO were associated with only one slow wave ('simple peak'), but the incidence of broad, irregular peaks belonging to more than one slow wave ('complex peaks') was significantly higher in CCK sequences (p < 0.02). Spectral analysis of SO pressure and slow-wave activity confirmed the dominating one-to-one relation between SO slow-wave and pressure peaks up to 1/4 IDU/kg, but also showed the disturbance caused by the increasing number of complex peaks generated by doses of at least 1/2 IDU/kg. CONCLUSIONS CCK increases SO and duodenal activity equally. Up to a CCK dose of 1/4 IDU/kg the SO slow-wave regulatory mechanism is undisturbed, but higher doses lead to a fall in slow-wave frequency and qualitative changes in the relation between SO pressure and slow-wave activity.