Homogenates of the submaxillary glands of mature domestic boars were incubated with radioactively labelled C19 steroids. The metabolism of [7α-3H]dehydroepiandrosterone and [7α-3H]androstenedione was primarily to the end products 5α-androstane-3,17-dione and androsterone, but some testosterone, 5α-dihydrotestosterone and 5α-androstane-3α,17β-diol were also formed. When [7α-3H]5-androstene-3β,17β-diol was used as a substrate, the major metabolite was testosterone. Both [7α-3H]5-androstene-3β,17β-diol and [1α,2α-3H]-testosterone were converted to 5α-dihydrotestosterone and high yields of 5α-androstane-3α,17β-diol, but only small yields of 5α-androstane-3β,17β-diol and androsterone were obtained. High yields of 5α-androstane-3α,17β-diol and to a lesser extent 5α-androstane-3β,17β-diol were formed from the substrate [1α,2α-3H]5α-dihydrotestosterone. Conversely, when both 3H-labelled androstanediols were used as substrates, 5α-dihydrotestosterone was formed in equal amounts together with a large yield of 5α-androstane-3α,17β-diol from the 3β-epimer. There was no evidence for steroid sulphatase or aromatase activity in these incubations. These findings support the prohormone concept that precursor steroids of testosterone, known to be present in boar testis, could act as an additional source of potent androgens in peripheral target organs to androgens in this species. In a number of incubations with [1α,2α-3H]testosterone, free oestradiol-17β and oestrone, but not oestrone sulphate enhanced the formation of androstenedione, but reduced the formation of 5α-dihydrotestosterone. However, both free and conjugated oestrogen reduced the formation of 5α-androstane-3α,17β-diol. These findings are discussed in relation to the high levels of oestrogen found in male pigs.