Saccharomyces cerevisiae (yeast) cells were employed as a source of alcohol dehydrogenase in the NAD+-to-NADH reaction. The cells were immobilized in calcium alginate monofilament fibers and used in a biological reactor. The alginate could not be heat sterilized since temperatures above 80 °C caused the polymer chains to degrade. The same proved true for the high pH necessary for the reaction, but the alginate strength was increased by Ba2+ solution treatment. X-ray probe analysis showed that about 30% of the Ca2+ sites exchanged with the Ba2+ ions. The Ba2+ ions (as well as the Ca2+ ions) permeabilized the cells and increased the reaction rate. Long term trials showed that Ba2+ ions were slowly elutriated from the fiber biocatalyst, causing a drop in reaction rate. The trend certainly was reversible as far as the fiber was concerned. It is assumed that the permeabilization of the cells by the Ba2+ ions was a reversible process.