Using the patch-clamp technique, two different ion channels have been characterized further in the human red blood cell (RBC) membrane. We demonstrate that the non-selective cation channel (NSC) is permeable to Ca 2 + and can be activated by prostaglandin E 2 (PGE 2 ). Therefore, the physiological role of this channel could be, together with the Ca 2 + -activated K + channel, the participation in the process of blood clot formation. We give also evidence that another channel in the RBC membrane, so far assumed to be a small conductance anion channel, is more likely to be a proton or a hydroxyl ion channel.