Since diagnostic value of double contrast colon imaging is dependent on the colon preparation used, tolerance and efficacy of 4 colon preparations were evaluated by a simple-blind, comparative, randomized study in 185 outpatients. Colon preparation involves variable combinations of 3 means: residue-free diet, laxatives and wash-out enemas. Principal criteria were evaluated under blind conditions by the same investigator during all examinations, with quantitative rating by segment (left, transverse and right colon) of adherence and colon cleanliness, and global assessment of quality of preparation. The 4 groups were comparable: mean age 44.7 years, sex ratio (male/female) 51.3%. Tolerance and compliance were elevated without significant inter-group differences. The colon preparations studied did not allow a homogeneous preparation to be obtained throughout the colon, efficacy in left colon being superior to right colon, whatever the method used. Analysis of cleanliness and adherence by segment failed to show significant differences between procedures, probably related to weak differences in their effectiveness and the strict nature of the study. The use of a global criterion tended to show value of wash-out enemas as a routine procedure, whether in outpatients or in the Radiology department.