Abstract: In this paper are reported the results of a diagnostic survey conducted on 112 adult layer chickens from a flock in which osteopathic leukosis (osteopetrosis) was occurring. Only 3 positive cases were detected on the basis of clinical signs,but on first attempt 45 positive cases were discovered by radiography of one hind limb. This represented a 16- fold increase in detection rate and revealed the incidence of the disease to be as high as 46. 39%(45/97). In the positive cases,lesions occurred in 100% of the tibiae examined whereas only 24. 44% of the metatarsi showed pathological changes. Measurements of tibial external diameter and bony cortex on radiographs of hind limbs from 97 chickens,showed that in 52 osteopetrosis-negative chickens,the mid -portion of the tibia had a normal average value of 6. 16 mm (5. 5-7. 0 mm) ,and that the normal average value for the thickness of the cortical osseous tissue was 0. 64 mm (0. 4 - 0. 9 mm). Of the 42 occult cases which accounted for 93. 33% of the 45 osteopetrosis-positive birds,the external diameter of the bone fell within normal values,but the average thickness of the cortical bone was 0. 81 mm (slight increase) and 2. 12 mm (moderate increase). In the 3 clinical cases which occupied 6. 67% of the affected chickens,the external diameter of the tibia exceeded 7. 5 mm,attaining even 14 mm,while the thickness of the cortical bone exceeded 1. 5 mm,reaching even 9 mm.