The incidence of colorectal cancer in Ashkenazi Jews is two to three times higher than in non-Ashkenazis. For a community colorectal screening program 1339 asymptomatic Ashkenazis over 40 yr old were asked to participate. Of these 1012 (75%) took Hemoccult II kits [fecal occult blood tests (FOBT)], and 614 (46%) personally returned them. Screenees were interviewed regarding family and personal medical history. Fourteen persons (2.3%) had positive tests, in whom colonoscopy revealed two with cancer (Dukes' B,C) and two with a greater than 2 cm polyp. The remaining 600 persons were invited for flexible sigmoidoscopy (FS) but only 287 (48%) appeared. The mean depth of insertion of the instrument was 50.3 cm (range 30-120), but was poorer for women. FS identified lesions in 28 (9.7%) persons: three had Dukes' A carcinomas and 25 had less than 2 cm adenomatous polyps. Significantly more women than men accepted FOBT, but among those completing FOBT, there was no difference by sex for use of FS. Middle-aged persons (50-69 yr) found screening more acceptable than young or older persons. Among screenees who agreed to undergo FS, a significantly larger fraction had a first relative with colon cancer, or a personal history of colon or female genital neoplasia, compared to those not agreeing to FS. There were no differences in screenees with relatives with noncolon cancer. Eighty-eight couples completed FOBT and were invited for FS. The decision whether or not to participate was made for both members in 81 (92%) couples. In conclusion, effective screening programs have to take into consideration compliance patterns of the target population.