Possible protective effects of Allium sativum and Crataegus--alone and in combination--on isoprenaline (isoproterenol)-induced heart, liver and pancreas damage were studied using rats as test animals. Pretreatment with Allium sativum alone, or in combination with Crataegus, resulted in protective effects on isoprenaline-induced damage of heart, liver, and pancreas. These effects proved to be dose-dependent. The following parameters were used to evaluate the protective effect: Clinical signs, qualitative histological and histoenzymatical findings, as well as quantitative microphotometric determination of enzymatic activities of succinate dehydrogenase, NADH-NBT reductase, acid phosphatase and glucose-6-phosphate dehydrogenase in cardiac, hepatic and pancreatic tissues. The underlying mechanisms are discussed. The results suggest that Allium sativum, resp. Allium sativum plus Crataegus exert a pronounced protective effect.