Elevated serum levels of peptides hormones in patients with acute leukemia and production of these agents by the leukemic blasts have been described. In 77 patients with acute leukemia the influence of common risk factors and elevations of serum levels of calcitonin-related peptides on clinical outcome was evaluated. By multivariate analysis, only age and elevated serum level of h-CT were found to be significantly correlated to survival. CGRP and s-CT showed no influence on outcome. Closer inspection of the clinical course of these patients showed that patients with elevated h-CT are not likely to survive the first 4 weeks after diagnosis. The possibility that this hormone may influence the biological behavior of the leukemic cells is discussed.