A group of 52 consecutive patients with polycythemia vera was submitted to long-term therapy with radioactive phosphorus (32P). Initial phase of therapy induced complete remissions (normalization of hematogram; spleen not palpable) in 45% of the patients, and partial remissions in the remaining 55%. During maintenance therapy of the complete remission group, mean remission time was about 3.5 years. Individual remission times ranged between 1 and 6 years. In the group of patients with incomplete remission, mean remission time increased with the progression of the disease due to gradual development of "spent" -polycythemia. In patients with splenomegaly, remission time was negatively correlated to spleen size. In both groups the increment of annual accumulated dose averaged 2.4 mCi 32P. When considering polycythemia related causes of death only, mean survival time attained 12 years after initial treatment with 32P. Acute leukemia occurred in 2 patients (4%).