The effects of methandrostenolone (M) and testosterone propionate (TP) were studied in hypophysectomized rats with or without supplementary treatment with growth hormone (GH). Dexamethasone (DEX), an anti-anabolic agent, and A-norprogesterone (ANP), a specific anti-androgen, were used to disassociate anabolic from androgenic activity. Qualitative differences in the actions of M and TP were evident. M required GH to stimulate growth of the levator ani muscle (LA), ventral prostate (VP) and seminal vesicles (SV) of hypophysectomized rats. whereas TP did not. Neither compound induced body weight gain in the absence of GH. GH alone accelerated body growth but did not influence relative organ or muscle weight. The effects of combined M and GH on LA weight were antagonized by DEX but not by ANP, whereas LA stimulation by TP plus GH was antagonized slightly by both ANP and DEX. Growth of the SV and VP induced by M plus GH was inhibited by either DEX or ANP whereas that by TP plus GH was only prevented by ANP. Th...