A technetium 99m diphosphonate scan is a sensitive detector of bony metastases of breast, prostate, and lung cancer. For these particular neoplasms, a negative bone scan in an asymptomatic patient is adequate evidence for absence of bony metastases and a correlative roentgenographic examination may not be necessary. Positive studies demonstrating multiple characteristic discrete areas of increased activity should be considered strong evidence for metastases. Single equivocal lesions require roentgenographic and occasionally biopsy correlation. If roentgenography fails to reveal the source of increased uptake, (e.g., degenerative disease) the scan lesion should remain suspicious for metastases.