The molecular weight of aspermatogenic antigen as determined by equilibrium ultracentrifugation.

The extraction of antigen from testis and sperm is described. This antigen, when administered in microgram amounts in a single injection, induces aspermatogenesis in 100% of guinea pigs so treated. The deletion of the seminiferous cell line is specific (no cross-reactions) and provides a tool for investigating inhibition of cell replication as well as reproductive control.