Osteopetrosis cured by temporary parabiosis.

The excessive accumulations of spongiosa in the long bones of congenitally osteopetrotic mice permanently disappeared after a brief parabiotic union to normal littermates. Most of the bone removal was accomplished long after interruption of parabiosis. It is proposed that, during parabiosis, progenitors of competent osteolytic cells were recruited from the blood of the normal mouse.