Abstract
Organ culture of tibias and femurs from 7-day chick embryos showed that at 2 hrs. bone contained 1.08 times as much Sr89 as Ca45. Within 7 days the observed ratio (bone-medium) in bone equilibrated at 0.83. Additional data indicated that Sr89 left bone at a ratio of 1.2 times that of Ca45. Carrier Sr markedly inhibited the uptake of Ca45 but the discriminatory mechanisms were unaltered.