The clinical records and imaging studies of 140 patients who had 57Co-bleomycin scans were reviewed. In 53% of the patients with known tumor at the time of examination, all clinically demonstrable lesions picked up cobalt. The success rate was particularly high in carcinoma of the lung (15 of 17) and gastrointestinal tract (12 of 17). The major role of cobalt bleomycin seems to be as an early screening test for metastases in patients with carcinoma of the lung, gastrointestinal tract, and uterus. The scan is most useful in demonstrating spread to the brain, liver, and adrenals.