Normal splenocytes cultured with Formalin-killed Candida albicans were shown to acquire significant suppressor cell activity in a period of 3 days. These cells were found to suppress both the phytohemagglutinin-induced mitogen response as well as the anti-sheep erythrocyte antibody response. Experiments were carried out to determine the nature of the suppressor cell population. Results showed that these cells were not susceptible to treatment with anti-Thy 1 antibody and complement. Panning experiments showed that the suppressor cells were not plastic-adherent or Mac-1 antigen-positive. The suppressor cells were, however, adherent to anti-mouse immunoglobulin (F(ab')2-fragment)-coated dishes. Additional experiments showed that the suppressor cell activity was susceptible to treatment with monoclonal anti-Lyb 2.1 antibody and complement. These results suggest that the suppressor cell induced in vitro by Candida is a member of the B-lymphocyte lineage.