THERE has been considerable speculation in recent years on the nature of the current carriers in electrical conductivity of proteins. Up to 1943, the prevailing opinion was that the conductivity of proteins with adsorbed water was ionic. Then Baxter1 suggested that his results were more consistent with an electronic conduction mechanism both in the dry and wet states. From their theoretical work, Evans and Gergely2 concluded that dry proteins should be electronic semi-conductors with an interband gap of about 3.0 eV. Proteins, in the dry and wet states, are indeed semiconductors, but with activation energies less than 3.0 eV. More recent experiments by King and Medley3 on very wet proteins (> 15 per cent adsorbed water) have shown that the passage of a d.c. current produces hydrogen by an electrolytic process in quantitative agreement with theory, Riehl4 has suggested that the conductivity of wet proteins is due to oriented water in an ice-like configuration. Cardew and Eley5 believe that dry proteins are electronic semi-conductors, and that in wet proteins the current carriers are probably protons.