In the present study, the effects of beta-adrenergic receptor agonists on the hydrogen peroxide (H2O2) production in phorbol myristate acetate stimulated guinea pig alveolar macrophage suspensions have been investigated. In contrast to suggestions described in literature, our results indicate that the H2O2 production in alveolar macrophage suspensions is not mediated by beta-adrenergic receptors. Rather, it is suggested that the inhibitory effect of catecholamines in the H2O2 formation which is found after 5 minutes is the result of inhibition of the horseradish peroxidase catalysed phenol red oxidation, used as H2O2 measurement, by the catecholamines.