Eight of a group of fourteen pure-bred young rabbits of the same age were treated over the left forelegs with 2,600 roentgens; the remaining six animals were used as controls. Roentgenograms of both forelegs of each animal were made at monthly intervals until growth in the controls had ceased. Growth in the radii and ulnae was followed by careful measurement of the roentgenograms for a period of eight months, giving a total of 369 observations. Sometime within the first month, growth in the treated bones stopped completely and did not reappear during the period of observation. Growth in the untreated bones of the experimental animals was not affected.