The gonadal and placental paralogues of porcine aromatase cytochrome P450 (P450arom) were examined for novel catalytic properties to shed light on the evolutionary survival of duplicated copies of an enzyme critical to reproduction. Recombinant gonadal P450arom catalyzed formation of a novel metabolite from testosterone, identified by GC-MS and biochemical analyses as 1-hydroxy-testosterone (1 OH-T), in almost equal proportion to estradiol-17 (E₂). This activity was absent in reactions with the porcine placental paralogue (or other orthologues) of P450arom, and was minimal with androstenedione. Incubations with both porcine enzymes, bovine and human P450arom demonstrated that 1OH-T was not aromatizable, and 1OH-T activated the androgen receptor of prostate cancer cells in vitro. Porcine testicular and follicular granulosa tissues synthesized 1OH-T which was also detected in testicular venous plasma. These results constitute the first of identification of a novel, perhaps potent, non-aromatizable metabolite of testosterone, whose synthesis (paradoxically) can be definitively ascribed to the activity of the gonadal paralogue of porcine P450arom. It likely represents an evolutionary gain of function associated with fixation and the survival of the genes after CYP19 duplication. Novel activities and adaptive functions may exist among other duplicated vertebrate aromatases.