T cells from mice painted with picryl chloride inhibit secondary IgG anti-TNP antibody responses of normal mice to the sensitizer. Like other suppressor T cells produced after painting which inhibit DNA synthesis and the generation of cytotoxic T cells, these cells could be produced in adult thymectomized mice but not by mice treated with high doses of cyclophosphamide (250 mg/kg). The cells had to be injected within 48 h of a primary painting to inhibit the response to challenge 2-3 weeks later. This associated with their ability to inhibit DNA synthesis in draining lymph nodes after a primary painting. Double transfer experiments using spleen and lymph node cells failed to show any further activation or induction of suppressor function after challenge with antigen. As judged by the ability of anti-theta treated cells from suppressed mice to function as anti TNP primed B cells in adoptive responses to TNP-KLH no defect in B-cell memory was found. When, however, the ability of painting with picryl chloride to prime for challenge with TNP-KLH was used as a measure of B-cell function in situ it was found that the cells could inhibit responses. Responses to primary and secondary injections of TNP-KLH were not inhibited.