Some parameters of rhythmic mechanical and electrical events of guinea-pig gall-bladder were investigated. Pressure-volume (P-V) responses, extracellular electrical activity and gall-bladder morphology were recorded. Rhythmic gall-bladder activity consisted of waves of pressure at intraluminal volumes between 0.5 and 1.8 ml. The pressure waveforms developed in a single contraction were usually oscillatory, containing two or more peaks which were more or less separated. The maximum amplitude value of phasic pressure waves was 1.8 +/- 0.6 cmH2O. Bursts of spike potentials appeared at three equidistant electrodes along the longitudinal diameter of the bladder with variable delays indicating absence of propagation of the fast electrical activity. By analysing the morphological changes of gall-bladder silhouette during the P-V curve it was evident that the maximum amplitude and duration of contractile events occurred when the whole muscular wall was stretched. Tetrodotoxin added to the bath solution did not abolish rhythmic activity--indicating its myogenic nature--and shifted the P-V curve to the left of the control, confirming the inhibitory role of the intrinsic nervous plexus of guinea-pig gall-bladder.