Seventy-two gilts (initial weight = 57.9 kg) were used to determine the interrelationship of porcine somatotropin (pST) administration and dietary P on growth performance of finishing gilts (58 to 106 kg) and the effect on bone mechanical properties and mineralization for a 35-d postfinishing phase after withdrawal of pST administration. Gilts were injected daily with placebo (control) or 4 mg of pST and fed .4, .6, or .8% P in the finishing phase. Administration of pST increased ADG and G/F (P < .01) and decreased ADFI (P < .01) during the finishing phase. Increasing dietary P resulted in increased (quadratic, P < .04) ADG from d 0 to 28 of the finishing phase; however, dietary P had no effect (P > .18) on ADG, G/F, or ADFI for the overall finishing phase. When each block weight averaged 106 kg, half the gilts were slaughtered and the first rib, femur, and third and fourth metacarpals were collected. Stress, modulus of elasticity, and ash content of rib, femur, and metacarpals were reduced (P < .06) and femur wall thickness was increased (P < .01) in pST-treated gilts. Increasing dietary P increased (linear, P < .05) bending moment, stress, and ash content for all bones collected, with the exception of metacarpal stress, which was not affected (P > .22). The remaining 36 gilts were individually fed 1.8 kg/d of a common diet to assure a P intake of 22.8 g/d for the 35-d postfinishing phase. Gilts that received higher levels of dietary P during the finishing phase had increased (linear, P < .06) bending moment and ash content for the rib and femur; rib stress, and femur wall thickness were also increased after the postfinishing phase. From d 0 to 28 of the finishing phase, pST-treated gilts required a diet with > .4% P (10.3 g/d P) to maximize growth performance. However, a diet with .4% P (12.44 and 10.66 g/d P, control and pST-treated, respectively) was adequate for growth performance during the overall finishing phase (56 to 106 kg).(ABSTRACT TRUNCATED AT 400 WORDS)