The ability of L-dopa to arrest pain can be used to predict objective response of skeletal disease to endocrine ablation or additive therapy. In the present study, 43 patients with painful skeletal metastases were evaluated for the relief of pain by L-dopa, given 250 mg to 500 mg orally every 4 hours for 4 days. Sixteen of the 25 responders to L-dopa had objective response to either previous or later hormonal therapy while all the 18 non-responders did not benefit from endocrine ablation. The results of L-dopa responses also correlated well to the presence of absence of cytoplasmic ER in tumor. These results demonstrate that both tests (L-dopa and ER) are reliable indicators, one complimenting the other, in prognosticating response to endocrine therapy and should be used prior to hormone treatment. Alternative therapy should be considered for patients who are non-responders to the L-dopa test and/or whose tumors contain negligible ER. The long term therapeutic value of L-Dopa, however, is limited.