Vitronectin is an adhesion protein present within the acrosomal cap region of human spermatozoa and is liberated during the acrosome reaction. The purpose of this study was to determine if vitronectin mRNA was synthesized in the male genital tract using the reverse transcriptase in-situ polymerase chain reaction (PCR) technique. Twelve genital tract tissues, which included six testes, one showing Sertoli cells only and one from a 3 year old boy, as well as sections from the prostate, seminal vesicles, and epididymis, were analysed for vitronectin transcripts. PCR-amplified vitronectin cDNA was detected in the seminiferous tubules of the four adult testes that showed normal spermatogenesis and localized to the spermatocytes and round spermatids. PCR-amplified vitronectin cDNA was not detected in the tissues of the prostate, epididymis, and seminal vesicles from the men whose testes did contain the message, nor in the testes with Sertoli cells only or that of the prepubertal boy. It is concluded that, in the male genital tract, vitronectin is transcribed exclusively in the germ cells at the spermatocyte and round spermatid stages. This demonstrates that the translated protein present in the spermatozoon is being produced in situ. Further study is needed to determine the role of this protein in the dynamics of sperm-oocyte interaction.