Male sterility due to abnormal sperm morphology or motion has been widely reported, although relatively little has been published on the sperm nuclear protein abnormalities. We report the first cases worldwide of infertile patients having a complete selective absence of protamine P2 in the sperm nucleus. This provides a selective phenotype that will aid understanding of the mechanisms of synthesis, processing, or function of the P2 protamines. In addition, it is of marked immediate relevance to medicine as it allows the diagnosis of this type of human male sterility and the opportunity to understand the basis of this defect.