Two experiments were conducted to determine the relative biological values (BV) of phosphorus in feed phosphates. Experiment 2 was a replicate of Experiment 1, except that an additional phosphate source was tested. Within experiments, each treatment was replicated twice. Each pen contained eight broiler cockerels. The experimental diets were composed primarily of corn and soybean meal. The reference phosphate [anhydrous, reagent-grade, dibasic calcium phosphate (AR-DCP)] was added to supply five levels of phosphorus. Each phosphate supplement was added to supply two levels of phosphorus. A regression equation was calculated based on logarithm g, nonphytate phosphorus per kilogram of diet versus the percentage of bone ash from chicks fed diets containing AR-DCP. Nonphytate phosphorus equivalents were calculated using the percentage of bone ash from chicks fed the test phosphates. The biological values of the test phosphates were determined as nonphytate phosphorus equivalents, minus the nonphytate phosphorus in the basal diet, divided by the amount of supplemental phosphorus. The BV obtained for the commercial phosphates in Experiments 1 and 2 were: dibasic calcium phosphate, 106 and 104; monobasic calcium phosphate. 102 and 104; defluorinated phosphate (DFP)-1, 88 and 90; and DFP-2, 100.