A variety of molecular techniques were used to search human and baboon gonadal tissues for evidence of transcription of the genes for the peptide hormones oxytocin and vasopressin. Only a highly sensitive assay based on a modification of the polymerase chain reaction succeeded in detecting mRNA copies of the oxytocin gene in both human and baboon corpus luteum. Vasopressin gene transcription was not detected in human testis and corpus luteum and was found only once in four different experiments in baboon corpus luteum. Evidence for oxytocin gene transcription in the human testis was found in three of five experiments. The method employed and subsequent sequence analysis of the polymerase products verified the presence of oxytocin mRNA with normal hypothalamic-type exonic structure in primate corpus luteum. Nevertheless, the very low levels of mRNA present are unlikely to support other than local functions for the encoded nonapeptide hormones.