One hundred ten consecutive patients undergoing 35-cm flexible sigmoidoscopy were enrolled in a study to compare the efficacy of one vs two enemas (Fleet's) in achieving adequate bowel preparation. Fifty-five patients received two enemas administered one and three hours before sigmoidoscopy. The other 55 subjects received one enema given one hour before the procedure. Bowel preparation was considered inadequate if sigmoidoscopy was terminated prematurely because fecal material obscured visualization through the sigmoidoscope. Inadequate bowel preparation occurred in 12.9 percent of subjects who received one enema and in 20.0 percent of those who received two enemas (chi 2 = 0.97, P = .36). There was no difference between the groups in depth of penetration of the sigmoidoscope or duration (in minutes) of the examination. It is concluded that either one or two enemas are equally effective in preparing patients for sigmoidoscopy. Patient acceptance of sigmoidoscopy could be enhanced by using one enema instead of two with no decrease in adequacy of bowel preparation.