Beta-endorphin and beta-lipotropin plasma concentrations were evaluated in 24 patients with congestive heart failure (CHF) (10 patients had chronic CHF and 14 an acute episode superimposing on chronic CHF), and in 35 age matched controls. Beta-endorphin and beta-lipotropin were significantly lower (P less than 0.005 and P less than 0.001 respectively) in patients with CHF than in controls. A significant decrease of both peptides vs controls was observed also in the two subgroups of patients, with chronic and acute CHF, without statistical differences between the subgroups. Beta-endorphin and beta-lipotropin showed a close and significant correlation (r = 0.88, P less than 0.001) amongst the whole series of patients as well as in both subgroups with chronic and acute CHF. In consideration of the long duration of the disease the decreased concentrations of beta-endorphin and beta-lipotropin can be considered to be due to a depletion of the releasable pool of the peptides, as it was previously shown for chronic stress.