To study whether reviewers aware of author identity are biased in favor of authors with more previous publications. Randomized controlled trial. Editorial office of the Journal of Developmental and Behavioral Pediatrics. Two "blinded" and two "nonblinded" reviewers assigned to 57 consecutive manuscripts submitted between September 1991 and March 1992. Spearman rank correlation coefficients were used to compare the sum of rating scores of 1 to 5 (1, accept; 5, reject) given by the two blinded reviewers, the two nonblinded reviewers, and the editors to the number of articles published previously by the first and senior authors (as determined from requested curricula vitae). Blinded reviewers were sent a questionnaire asking whether they could determine the identity of the authors, how they knew, and whether they thought binding changed the quality or difficulty of their review. The Wilcoxon Sign Rank Test disclosed no differences between blinded and nonblinded scores. The number of previous articles by the senior author was significantly correlated (P < .01) with blinded scores (r = -.45) and editors' decisions (r = -.45), but not with nonblinded scores; the number of articles by the first author was correlated (P < .05) with editors' decisions (r = -.35) but not with blinded or nonblinded scores. Fifty (46%) of 108 blinded reviewers correctly guessed the identity of the authors, mostly from self-references and knowledge of the work; 86% believed blinding did not change the quality of their review, and 73% believed it did not change the difficulty of performing a review. Blinded reviewers and editors in this study, but not nonblinded reviewers, gave better scores to authors with more previous articles. These results suggest that blinded reviewers may provide more unbiased reviews and that nonblinded reviewers may be affected by various types of bias.