Little is known about the factors that determine the extent of dispersion of enema solutions in the colon. To unravel some of the determinants we evaluated a consecutive series of patients with left-sided colitis. 40 ml enema solutions, viscosity 0.062 Pa.s (62 cP) at 37 degrees C were labelled with 10 MBq 99m-technetium human serum albumin microcolloid. Scintigraphic imaging was performed in 35 patients until 2 hours after administration of the enema. In 8 of the 16 patients with limited retrograde spread the study was repeated after doubling the volume (80 ml). We conclude that the extent of dispersion of an enema 0.062 Pa.s solution is highly variable. The basic fluid component for therapeutic 40 ml enemas (viscosity 0.062 Pa.s) reaches the affected area in patients with left sided colitis only in 40% of the cases. Increasing the volume of the enema can be an effective way to increase the retrograde spread up to the affected area in patients with limited retrograde spread. Scintigraphic imaging is a simple and reliable method of checking whether an enema conforms to the requirements of medical treatment. Scintigraphic imaging lasting for 1 hour after administration of the enema appears to suffice.