To determine growth performance during and after injection of recombinant porcine somatotropin (rpSt), crossbred Yorkshire gilts and barrows (n = 54/gender, 27 to 42 kg BW) were blocked by BW and gender (n = 3 blocks/gender). Within each block, three pigs/gender were assigned randomly to each of six pens/block. A diet containing 24.8% CP was fed ad libitum. During the live weight period of 30 to 110 kg, pigs either remained as controls (one pen/block) or were injected (i.m.) daily with rpSt (120 micrograms/kg BW) during either 30 to 60, 30 to 100, 30 to 110, 60 to 100 or 60 to 110 kg BW. Thus, three gilts and three barrows in each of three pens received each treatment. Pigs were slaughtered at either 60 kg BW (1 d after rpSt injection) or 110 kg BW (1 d, 10 d or 70 d after rpSt injection). Relative to controls, pigs injected with rpSt exhibited faster and more efficient growth during the injection period (P less than .05) but slower and less efficient growth during 10 d after cessation of injection (P less than .05). Carcasses of pigs slaughtered 1 d or 10 d after rpSt injection were leaner than controls (P less than .05), but among the pigs treated with rpSt, carcasses of pigs withdrawn from rpSt for 10 d contained more fat (P less than .05) and had a lower percentage of muscle (P less than .05) than carcasses of pigs withdrawn from rpSt for 1 d. Growth and carcass measurements were similar (P greater than .05) between controls and pigs killed 70 d after rpSt injection.(ABSTRACT TRUNCATED AT 250 WORDS)