The hematopoietic system is a source of odorants that distinguish major histocompatibility types.

Radiation chimeras were made by restoring lethally irradiated inbred mice with bone marrow cells of F1 hybrid mice of crosses between that inbred strain and an H-2-congenic strain. The urine of these chimeras was tested by the Y maze method, and shown to have acquired a scent indicative of the reconstituting donors' H-2 type. Thus, cells of the hematopoietic system contribute to the H-2-related odorant properties that enable mice to distinguish one another according to their H-2 types.