Sixteen patients with 20 lesions of Paget's disease of bone were studied with bone marrow scintigraphy (colloid), bone tissue scintigraphy and radiography. Bone marrow scintigraphy showed normal or increased colloid uptake in 15 of 20 pagetic lesions, and decreased uptake in 4. Bone tissue scintigraphy showed increased metabolic activity in all lesions and was useful in detecting polyostotic disease as well as the extent of the lesions. Conventional radiography most often showed the typical appearance of Paget's disease, but the changes observed were sometimes difficult to differentiate from malignant disease. However, a preserved or increased reticuloendothelial function in the pagetic lesion contradicts metastatic disease as a differential diagnosis. Bone marrow scintigraphy with radiocolloid is a valuable method in the analysis of Paget's disease of bone.