A soluble membrane component of type III pneumococcal polysaccharide-coupled spleen cells (S3-SCSM) induces S3-specific suppressor T cells (Ts) in mice. These Ts can be detected only if mice are pretreated with cyclophosphamide (Cy) or if cells adherent to the lectin Vicia villosa are removed from the spleen cell population prior to transfer. The V. villosa-adherent spleen cells from mice injected with S3-SCSM could abrogate suppression mediated by Ts induced by S3-SCSM in Cy-treated mice. The V. villosa-adherent contrasuppressor cells were shown to be T cells that were I-J+ and of the Lyt-1 phenotype. Contrasuppressor T cells (Tcs) were not present in V. villosa-adherent spleen cell fractions obtained from normal mice, from mice injected with polyvinylpyrrolidone-coupled spleen cells, or from Cy-treated mice injected with S3-SCSM, i.e., mice in which Ts activity is dominant. The V. villosa-adherent cells that abrogated the activity of Ts induced by S3-SCSM in Cy-treated mice did not abrogate suppression mediated by a different subset of S3-specific Ts, suggesting that the Tcs described here do not have activity against all Ts subsets. The ability of S3-SCSM to activate Tcs in normal mice provides an explanation for the inability to detect S3-specific Ts in several previous studies.