In a prospective double-blind study of the effectiveness and patient acceptance of Golytely whole-gut preparation for colonoscopy, 50 consecutive patients were randomly allocated to drink either 1.5 l (Group I) or 3 l (Group II). The patients had some slight dietary restrictions, and received mild laxatives on the preceding day. The cleansing result did not differ significantly in the two groups. The result was assessed as "good" in 76% of cases in Group I (95% confidence limits 55-91%) and in 83% of cases in Group II (95% confidence limits 63-95%). In half of the remaining cases in both groups the result was "acceptable" and in the other half "poor". Patient acceptance did not differ significantly in the two groups. After completion of the randomized study, oral cleansing with 1.5 l Golytely has been our daily routine. In 42 patients so treated quality of cleansing was good in 81% (95% confidence limits 66-91%), acceptable in 12%, and poor in 7%.