A Danish, randomized study with Hemoccult-II, including 60,000 persons between 45 and 74 years old, began in 1985. Methods of increasing acceptability are described for the first 8000. The first 1000 refusals are also analyzed. Written invitations including prestamped envelopes for return of the slides resulted in an acceptability of 58.8%. Two reminders increased the figure to 65.6%. Personal attempts to change the mind of those refusing increased the last figure to 68.9%. Incomplete slides were returned by 49 persons, but on request 43 sent a complete set. All 78 persons with positive tests had colonoscopy, which detected carcinomas in 10 and adenomas in 39. The study confirmed that results of trials from different countries are difficult to compare because of major differences among populations and methods. However, the present results were similar to those obtained in a Swedish study including only persons between 60 and 64 years old.