Activation of neutrophils induces generation of reactive oxygen species and release of granule enzymes, which not only participate in the bactericidal mechanisms of these cells, but also in possible tissue damage. We studied the effect of carvedilol (CARV) [0.1-100 micromol/l], an antihypertensive and cardiovascular drug with antioxidative properties, on superoxide generation (SO) and myeloperoxidase (MPO) release from isolated human neutrophils stimulated with fMLP, a specific receptor activator, or with PMA, a receptor bypassing stimulus. Unstimulated cells showed neither SO formation nor MPO release after preincubation with drug. CARV decreased fMLP and PMA stimulated MPO release and SO generation dose dependently. The inhibitory effect of CARV may attributed to non-specific action since its effect was not influenced by the type of stimulation. It might inhibit SO generation as well as MPO release either by membrane-operating stimulus (fMLP) or membrane bypassing activator (PMA).