The investigation was carried out on 90 broiler chickens receiving experimental low-phosphorus starter diets until day 21 of life: C, control; D, with the addition of 750 phytase units/kg; and R, without vitamin D₃ supplemented with 3 µg 1,25(OH)₂D₃ and 750 PTU/kg. On day 21, 15 chickens from each treatment were killed. Humeri and femora were isolated, weighed and physical and geometrical parameters of bones were determined. Bone mass and length in both experimental groups were similar, but showed greater values in relation to controls. The femora and humeri of control and experimental chickens showed significant differences in physical parameters. The values of geometrical parameters in the experimental group were higher than in the control, but not significantly in either of the experimental groups. Bone breaking strength was significantly affected by the combined addition of 1,25(OH)₂D₃ and phytase to the diet without vitamin D₃ as compared with the diet with phytase and adequate level of vitamin D₃.