Previous studies have shown that mouse CD8+ T lymphocyte clones (TLC) produce T cell-specific serine proteinase-1 (MTSP-1) as well as a family of six homologous molecules, termed granzymes B - G, which are structurally related to serine proteinases. Of these proteins, only MTSP-1 has been studied in detail. It has been shown to occur in the majority of CD8+ and a fraction of CD4+ T effector cells in vivo and in vitro and has demonstrable enzyme activity in these cells. The presence of the other serine proteinase-like molecules in T cells is less well defined. We have now analyzed the expression of mRNA species specific for granzymes B - G in activated T cell populations using the sensitive polymerase chain reaction which allows the detection of mRNA species from as little as 2 pg of total cytoplasmic RNA. We demonstrate that MTSP-1 and all six serine proteinase-like transcripts are expressed in a panel of four CD8+ and six CD4+ long-term-cultured TLC, though at greatly differing concentrations. In contrast, in vivo primed T cells of both phenotypes, CD4+ and CD8+, and in vitro activated T cells derived from short-term cultures only express mRNA species specific for MTSP-1 and CCP1 and little of those for CCP2, but no transcripts for granzymes D - G. These findings argue against the participation of granzymes D - G in T cell-mediated functions in vivo.