Three trials, involving 300 pigs were conducted to evaluate the effect of feeding 70 to 130% of the NRC recommended Ca/P levels from weaning to market weight on the relationships between measures of Ca/P status of postweaning swine, and to derive response surfaces relating diet and time effects to observed performance and bone characteristics. Pigs were slaughtered every 4 weeks following the start of the trials to obtain third and fourth metacarpals and metatarsals. Asymptotic response surfaces, relating the effects of dietary Ca/P level and time on test to the observed performance or bone characteristics were derived. The estimated lack of fit was significant for many criteria, although the magnitude of difference in fit appeared to be very small; therefore, the asymptotic response surfaces were found to reflect well the response of performance and bone criteria to dietary Ca/P levels of 70 to 130% of NRC recommendations over the period from weaning to market. The Ca/P level associated with 95 and 98% of maximum bone length, wet weight, radius and dry fat- free ash percentage of bones appeared to be the same or lower than that required to maximize body weight, average daily gain and feed intake; the performance criteria reached near maximum for Ca/P levels approximating the NRC recommendations. Bone wall thickness, cross—sectional area, bending and shear force, bending and shear stress, extracted weight of bone, and dry fat-free ash weight appeared to require higher Ca/P levels than recommended by NRC to reach 95 or 98% of maximum. Seventy-five pigs were biopsied at 4 week intervals, and a biopsy sample was also taken from 225 pigs at slaughter, to evaluate a bone biopsy procedure for use as a live-animal sampling method in swine nutrition studies. Biopsy cores from the live and the slaughter pigs were similar, indicating that repeated sampling of the live animal did not significantly alter the composition of the biopsy core. Biopsy core measures were significantly correlated with intact third and fourth metacarpal and metatarsal bone measures. Comparisons of the least squares means and standard errors of biopsy core and bone dry fat-free ash percentage indicated that the biopsy procedure may be more useful when NRC recommended or higher Ca/P levels are fed. There was strong indications, however, that use of the biopsy procedure warrants further consideration. / Ph. D.