Since the publication in this Journal of a description of the effects of placebos in rheumatoid conditions (Traut and Passerelli, 1957), there has been a growing literature on the subject of placebo responses, but little has appeared in print regarding such effects in arthritis. During a recent intra-articular injection trial in which two steroid preparations and a placebo were compared, it became apparent that responses to the latter were frequent and well marked. It was decided, therefore, to make a parallel study of the whole question of placebo responses as these occurred during the trial. The results of injection of the two steroids have already been reported; one paper dealt with the effects on rheumatoid arthritics (Chandler, Wright, and Hartfall, 1958) and the other with the effects on osteo-arthritics (Wright, Chandler, Morison, and Hartfall, 1960). The present paper is concerned chiefly with a detailed examination of the responses to the placebo injections in the same trial. It also reports the results of a subsequent dummy tablet trial on the same group of patients. Finally, some of the implications of these findings as they apply to clinical trials are discussed.