Heritabilities of and genetic, environmental, and phenotypic correlations among serum amounts of calcium, phosphorus, and magnesium and weight at weaning (WCa, WP, WMg, and WW, respectively) were estimated for an Angus (A)-Brahman(B) multibreed herd located at the Pine Acres Research Station of the University of Florida, Citra. Records were obtained from 380 calves produced by mating A, .75A .25B, .5A .5B, .25A .75B, B, and Brangus sires across dams of the same breed groups, except for .25A .75B, during 1989 and 1990. Restricted maximum likelihood procedures were used to compute variance and covariance components. Estimates of heritability were .39 (WCa), .40 (WP), .36 (WMg), and .35 (WW). Estimates of genetic, environmental, and phenotypic correlations were .66, .55, .57 (WCa, WP), .70, .71, .70 (WCa, WMg), 1.00, .86, .88 (WCa, WW), .50, .51, .51 (WP, WMg), .78, .60, .63 (WP, WW), and .86, .73, .75 (WMg, WW). These correlations indicate that serum Ca, P, and Mg could be used in multiple-trait genetic evaluation procedures to help identify animals that require low amounts of these macrominerals for preweaning growth. This may prove advantageous in mineral-deficient regions.