The effect of pamidronate treatment on the first development of bone metastases was investigated in 124 patients with breast cancer, with either locally advanced disease (n = 33) or extraskeletal metastases (n = 91), but no bone metastases in a randomised, multicentre, open controlled study. Patients were assigned to treatment with oral pamidronate, 300 mg/day, (n = 65) or to a control group (n = 59). Tumour therapy was freely allowed. A first clinical event of skeletal morbidity occurred in 22% pamidronate and 20% control patients; unequivocal first radiological manifestation of bone metastases was found in 36% pamidronate and 27% control patients (n.s.). The actuarial risk of a first skeletal event was similar in both groups. Quality-of-life measurements of bone metastases-related aspects showed no differences between the two groups. 19 patients withdrew from the study because of gastrointestinal complaints attributed to pamidronate. We conclude that supportive oral pamidronate treatment (300 mg/day) does not prevent nor delay the development of bone metastases in breast cancer patients at risk.