Inflammation suppresses phasic contractile activity in vivo. We investigated whether inflammation also suppresses in vitro phasic contractile activity and, if so, whether this could in part be due to the alteration of specific slow wave characteristics and morphology of the interstitial cells of Cajal (ICC). Circular muscle strips were obtained from normal and inflamed distal canine colon. Inflammation was induced by mucosal exposure to ethanol and acetic acid. The amplitudes of spontaneous, methacholine-induced, substance P-induced, and electrical field stimulation-induced contractions were smaller in inflamed muscle strips than in normal muscle strips. Inflammation reduced the resting membrane potential and the amplitude and duration of slow waves in circular muscle cells. Inflammation did not affect the amplitude of inhibitory junction potentials but did decrease their duration. Ultrastructural studies showed expansion of the extracellular space between circular muscle cells, reduction in the density of ICC and associated neural structures, damage to ICC processes, vacuolization of their cytoplasm, and blebbings of the plasma membrane. We conclude that inflammation-induced alterations of slow wave characteristics contribute to the suppression of phasic contractions. These alterations may, in part, be due to the damage to ICC. Inflammation impairs both the myogenic and neural regulation of phasic contractions.