Suppressor T cell product, which depresses the passive transfer of contact sensitivity, shares epitope(s) with the major histocompatibility complex.

Specific suppressor T cell product appears in the supernatant of cultures of lymph node cells of mice injected with picryl sulphonic acid and then painted with picryl chloride. It is detected by its ability to depress the passive transfer of contact sensitivity by immune cells incubated in it. This communication shows that the product can be absorbed by antisera prepared against the major histocompatibility locus but not by antisera prepared against mouse immunoglobulin.