Zinc is readily inserted into protoporphyrin suspended either in a salt-sucrose buffered solution or endogenously present in red cell haemolysate in erythropoietic protoporphyria. Red cells from healthy persons were incubated with metal-free protoporphyrin or zinc-protoporphyrin and irradiated with light at 360-470 nm. The photohaemolysis was significantly less with zinc-protoporphyrin compared with that of the metal-free protoporphyrin. The results are discusssed in relation to the possibility of using zinc as a photoprotective and hepatoprotective agent in erythropoietic protoporphyria.