Previous research in our laboratory demonstrated marked increases in phytate P utilization when P-deficient corn-soybean meal diets were supplemented with 1a-hydroxycholecalciferol [1alpha-(OH) D3] and fed to chicks. Our objective was to determine if 1alpha-(OH) D3 would improve phytate P utilization when supplemented to vitamin D-adequate laying hen diets. The five experimental treatments were 1) P-deficient corn-soybean basal diet [17% CP, 3.8% Ca, and 0.10% nonphytate NPP)], 2) basal with 2.5 microg/kg 1alpha-(OH) D3, 3) basal with 5 microg/kg 1alpha-(OH) D3, 4) basal with 10 microg/kg 1alpha-(OH) D3, and 5) basal with 0.35% supplemental inorganic P (0.45% NPP, positive control). Diets were fed to six replicate groups of 12 HyLine W-98 White Leghorn laying hens from 44 to 52 wk of age. Hen-day egg production was significantly depressed by 47 wk of age for the basal diet treatment and by 47, 49, and 48 wk of age, respectively, for the 2.5, 5, and 10 microg/kg of 1alpha-(OH) D3 treatments compared to the positive control diet. Supplementation with 5 or 10 microg/kg 1alpha-(OH) D3 did improve (P < 0.05) egg production, but egg production for those treatments was much lower than that for the 0.45% NPP treatment. Our results indicate that 1alpha-(OH) D3 did not substantially improve P utilization in laying hens fed corn-soybean meal diets.