In a prospective study 59 consecutive outpatients having double-contrast barium enemas (DCBE) were randomised into four groups. Each group had their enema performed at either a 15, 30, 45 or 60 minute interval following the end of a 1.5 litre cleansing water enema. Review of the films by two radiologists demonstrated that adequate mucosal coating was obtained after 45 minutes. The DCBE should therefore be performed at a minimum time interval of 45 minutes following colonic lavage, and not beforehand.