A previously pilot study of treatment with transfer factor in 3 patients with juvenile rheumatoid arthritis (JRA) gave promising results. However, in this small and open study no definite conclusions could be drawn. Therefore, a double-blind group trial was performed in 12 JRA patients treated with transfer factor, and in 12 placebo-treated control patients. The patients were evaluated clinically, by laboratory tests, and by estimation of different lymphocyte populations and cell-mediated immunity in vitro and in vivo. Transfer factor was not found to be of significant therapeutic value in patients with JRA. The only statistically significant difference between the two groups was a greater reduction in the percentage of T lymphocytes in transfer factor-treated patients than in control patients. The significance of this is difficult to explain and could have appeared by chance. No side effects of treatment with transfer factor were noted.