Possibly the greatest threat to the success of a randomized clinical
trial is the inability to recruit an adequate number of subjects. Concern
that the randomized clinical trial will adversely affect the
physician-patient relationship is the most common reason for physicians'
reluctance to enroll patients in such trials. We report a modification of a
prerandomized design, first described by Zelen, which was implemented in a
randomized clinical trial of arthroscopy for patients who had
osteoarthrosis of the knee. The method was associated with a sixfold
increase in the rate of accrual of patients as compared with the use of a
classic randomization trial. We propose the design as a potential solution
to the problem of recruitment of subjects, particularly for clinical
studies.