Clenbuterol 10(-8) to 10(-6) M inhibited antigen-induced histamine release from passively sensitized human lung tissue. This inhibition was not antagonized by propranolol, whereas the inhibitions observed with isoprenaline and fenoterol were reduced by propranolol. Clenbuterol also inhibited compound 48/80-induced histamine release and immunological histamine secretion from actively sensitized peritoneal rat mast cells. High concentrations of clenbuterol were required (10(-5) to 10(-3) M) and propranolol did not antagonize these inhibitions of histamine release. Isoprenaline and salbutamol did not modify the secretion from rat mast cells. The potential anti-anaphylactic activity of clenbuterol, might be partly related to its calcium antagonist property.