Data on 1,601 patients with node-positive operable breast cancer who were randomized in four different prospective adjuvant therapy trials were analyzed to evaluate the role of routine bone scans and the alkaline phosphatase value at regular intervals in screening for bone involvement. Bone scan was a prerequisite for randomization and was repeated within the first 12 months in 90% (1,441) of the patients. Abnormal or doubtful scan findings had to be verified by x-ray examination. The repeated scan results were normal in 1,263 (87.8%) patients, doubtful but with no radiologic evidence of bone metastasis in 161 (11%), and abnormal (radiologically confirmed) in 17 (1.2%). After a median observation of 4 years bone metastases as the first relapse developed in 136 (8.5%) patients. This occurred in 87 of 1,263 (6.9%) of the patients with normal repeated scan results and in 18 of 161 (11.2%) of those with doubtful repeated scan findings. Based on the results of the first repeated scan, early detection of a first recurrence in bone might have been possible for 2.4% of the population. Serum alkaline phosphatase levels were also without clinical use. Bone scan in the observation of patients with operable breast cancer should be performed only as dictated by the clinical situation.