Whole cells of Alcaligenes eutrophus (as well as isolated P. oxalaticus formate dehydrogenase and A. eutrophus hydrogenase coupled via NAD+ or methyl viologen) have been shown to produce H2 from formic acid. Immobilization of the cells in kappacarrageenan gel greatly enhances their stability at room temperature. The rate of hydrogen production catalyzed by immobilized A. eutrophus has been studied as a function of the concentrations of the cells and formate and also pH. An inhibition by high concentrations of formate has been found. Immobilized cells were also capable of synthesizingformate from H2 and bicarbonate. Yields of formate up to 30% have been obtained. The catalytic efficiency of immobilized A. eutrophus cells was compared with that of palladium adsorbed on activated carbon.