A monolayer absorption technique was used to test the hypothesis that killer cells directed to self HLA-associated minor histocompatibility antigens (H-Y) were divisible into subsets. The results showed that sensitized killer cells, which recognized two combined antigens HLA-A2; H-Y and HLA-B7; H-Y could indeed be divided into two populations. One was directed to HLA-A2; H-Y and the other to HLA-B7; H-Y. These results can be interpreted in the context of the altered self hypothesis. However, when interpreted in the context of the dual recognition hypothesis, they strongly suggest that independant clones of killer T cells exist which are committed to the recognition of self HLA.