Various aspects, mechanisms and functions of the oxidative burst with generation of O - 2 superoxide anions in plant cells, which is stimulated by active defence-inducing agents such as fungal infection or elicitor treatment, were reviewed mainly on the basis of experimental evidence obtained in a system of Solanaceae plants and Phytophthora spp. The oxidative burst may be due to an O - 2 -generating NADPH oxidase in the plasma membrane, which is activated with combinations of cytosolic proteins, Ca 2 + , calmodulin and protein kinase, following stimulation by elicitor molecules. The oxidative burst may play the role of an internal emergency signal for induction of the metabolic cascade for active defence.