Serum samples were obtained from 26 beef cows with uterine prolapse and from 15 with minor dystocia (controls). The serum of animals with uterine prolapse had significantly lower calcium concentration (mean +/- S.D. = 8,22 +/- 0,69 mg/dL, P</=0,01), higher phosphorus concentration (mean +/- S.D. = 4,78 +/- 1,75 mg/dL, P</=0,05) and lower calcium to phosphorus ratios (mean +/- S.D. = 1,99 +/- 0,88, P</=0,01) than for the control animals (means +/- S.D. = 8,91 +/- 0,75 mg/dL, 3,54 +/- 1,41 mg/dL and 2,99 +/- 1,41 respectively). Mild hypocalcemia (6,9 mg/dL-7,9 mg/dL) was present in 11 (42,3%) of the cows with prolapse as compared to only one (6,7%) of the controls. Hypophosphatemia was present in 11 (42,3%) of the animals with prolapse and in ten (66,7%) of the controls. Eighteen (69,2%) of the animals with prolapse were alert and ambulatory when treated and 15 (57,7%) were known to have required help to deliver the calf. Of the cattle group with uterine prolapse, 14 (53,8%) were two years old, six (23,1%) were three years old, and six (23,1%) were four years of age or older. It was concluded that mild hypocalcemia and some degree of dystocia were associated with the uterine prolapses. The phosphorus results were equivocal but the high incidence of hypophosphatemia may reflect a phosphorus deficient diet.