We analyzed 110 patients with metastatic prostate cancer (stage D2) to determine the associations between interval until progression and the pretreatment testosterone level, extent of bone metastases, performance status, race, age and pretreatment level of prostatic acid phosphatase. The median followup was 21 months (4 to 89 months). All patients received androgen deprivation therapy when metastases were identified. This multivariate analysis demonstrated that the pretreatment serum testosterone was the most significant variable (p less than 0.01) associated with interval until progression and the extent of bone metastases observed on the bone scan was the second most important variable (p less than 0.05). Age, race and prostatic acid phosphatase were not significantly correlated with the interval free of progression. Performance status was significantly correlated but it was nonsignificant in the multivariate analysis if the model already included testosterone level and extent of metastasis. Patients with a pretreatment testosterone level of less than 300 ng. per 100 ml. and more than 6 areas of increased uptake on the bone scan had the most rapid progression. We conclude that serum testosterone and extent of bone metastases are the most important of the analyzed factors in terms of interval to progression in patients with prostate cancer following androgen deprivation.