Malaria-infected human erythrocytes develop organic osmolyte channels, which provide the intraerythrocytic parasite with nutrients and dispose off metabolic waste products. The channels are dependent on purinoceptor signalling and irreversibly degraded by trypsin and chymotrypsin. Chymotrypsinized infected erythrocytes re-develop the osmolyte channels when post- cultivated indicative of a parasite-derived origin of the channels. Oxidized uninfected erythrocytes develop similar osmolyte channels. Here we show that chymotrypsin pre-treatment failed to prevent induction of the osmolyte channel in oxidized uninfected erythrocytes. Post-oxidation treatment, in sharp contrast, abolished the channel induction. Oxidized and chymotrypsin post- treated erythrocytes, however, slowly acquired osmolyte channels when further incubated in protease-free medium. One explanation for this behavior might be that chymotrypsin has only accesses to its cleavage site(s) in activated channels which are recruited from a pool of abundant 'silent' erythrocyte proteins. We further tested the role of cytosolic free Ca2+ and protein kinase C in the channel induction. Chelating Ca2+ in the medium inhibited channel induction in oxidized erythrocytes while Ca2+ permeabilization and phorbolester stimulation of non-oxidized cells induced channel activity. In conclusion, the intraerythrocytic malaria parasite utilizes an osmolyte permeability of its host cell possibly by interfering with erythrocyte Ca2+ - and protein kinase C signaling.