We investigated the effect of sustained-release implant administration of porcine somatotropin (pST) (4 mg/d) to male pigs for different lengths of time before slaughter. Crossbred white boars were assigned to six groups (n = 10/ group); B0, non-implanted boars; B6, boars implanted from 22 to 28 wk of age; B12, boars implanted from 16 to 28 wk of age; B18, boars implanted from 10 to 28 wk of age;C0, non-implanted castrates; and C18, castrates implanted from 10 to 28 wk of age. Castration was at 65 d of age. All pigs were slaughtered at 28 wk of age, and measures of offal and carcass components were recorded. Loin chops were collected for sensory evaluation. During the trial the pigs were maintained in individual pens with ad libitum access to water and a 19% CP corn-soybean meal diet containing 1.08% calculated lysine. Although pST reduced feed intake in castrates (P < .01), the effect in boars was nonsignificant. Slaughter weight was increased in a linear (P < .04) manner with length of pST treatment of boars, and slaughter weights of castrates given pST were greater (P < .01) than those of control castrates. The product of the changes in feed intake and gain resulted in greater efficiency of gain in pST-treated pigs than in control pigs (P < .01). A linear effect (P < .06) of length of pST treatment on trimmed lean cut weights of boars was noted. The weights of trimmed lean cuts produced by castrates treated for 18 wk with pST and boars treated for 12 or 18 wk were similar. Boars given pST for 18 wk had improved (P < .10) boar taint scores compared with untreated boars. Boars and castrates given pST for 18 wk had a similar rates of gain and weights of trimmed lean cuts. Efficiencies of gain were greater in pST-treated boars and castrates than in untreated boars, which were superior to untreated castrates in efficiency of gain.