[en] Localized areas of decreased radioactivity in the bone were demonstrated in 17 cases (1.4%) of 1,213 bone scintigrams performed with Tc-99m diphosphonate. In 15 out of 17 cases ''cold'' bone lesions were found to be metastatic bone cancers. Primary sites of cancers included the lung (7 cases), uterine cervix (3 cases), thyroid (2 cases), kidney (1 case), prostate (1 case) and pancreas (1 case). Other two lesions were found in primary site of chondroblastoma and metastatic site of osteosarcoma. Histological studies revealed squamous cell carcinoma in all 7 patients with lung cancer. Whereas ''hot'' bone lesions were found in 56% of adenocarcinoma and 31% of squamous cell carcinoma of the lung. High incidence of ''cold'' bone lesions were found in 3 (21%) out of 14 patients with cervical cancer who revealed positive bone scans. Abnormal bone scintigrams were found in 50 of 160 cases with breast cancer, but none of them showed ''cold'' bone lesions. In 14 cases increased uptake of radioactivity is noted around the cold lesions. Increased Ga-67 uptake in the ''cold'' lesion was found in 6 cases of lung cancer. Increased uptake of Tl-201 was found in the ''cold'' lesions in two patients with thyroid cancer. Postulated factors causing cold bone lesions were discussed reviewing literatures. (author)