BACKGROUND: Adrenaline is known to inhibit the immunological activation of human basophils. The same effect can be obtained with ultra-low doses of histamine.MATERIAL/METHODS: The present investigation was undertaken to verify the effects of ultra-low doses of adrenaline on the immunological activation of human basophils. For this purpose, purified human basophils were isolated from the blood of atopic donors and the response of the basophils to anti-IgE antiserum was evaluated by measuring the release of histamine and the expressions of the activation markers CD63 and CD203c on the basophil surface.RESULTS: The antigenic activation of basophils was significantly decreased by adrenaline at both pharmacological and ultra-low doses. The inhibiting effects of adrenaline were reversed by the beta blocker propranolol at either dose level.CONCLUSIONS: Although seemingly unexplainable by the currently accepted pharmacological principles, this phenomenon, already reported for histamine, deserves further investigation.