Forty-five pigs with an average initial live weight of 60 kg were used to investigate the effects of daily exogenous porcine pituitary growth hormone administration at two dose levels (pGH; 0, excipient buffer injected, and 100 micrograms.kg-1.d-1) for a 31-d period on the performance and body composition of boars, gilts and barrows allowed to consume feed ad libitum. Excipient boars consumed less feed, exhibited faster and more efficient growth (P less than .01) and produced less fat and more protein and water (P less than .01) in the empty body compared with excipient barrows, which in turn contained more fat and less water (P less than .05) in the empty body than did excipient gilts. These differences were largely eliminated by pGH administration, which induced differential effects in growth performance and body composition in boars, gilts and barrows. Growth hormone administration improved growth rate by 13, 22 and 16% and feed conversion efficiency by 19, 34 and 32% in boars, gilts and barrows, respectively. The reduction of body fat content (g/kg) elicited by pGH was 22, 36 and 33% for boars, gilts and barrows, respectively, with a corresponding increase (P less than .01) of body protein and water content. The magnitude of the pGH responses was greatest for gilts and barrows compared with boars, negating intrinsic sex-effect differences in growth performance and body composition of pigs. Pigs used in this study and treated with pGH exhibited a rate of protein deposition (approximately 225 g/d) far greater than previously reported, and as such redefine the genetic capacity for lean tissue growth by the pig.