In comparing ethanol production by free and Ca-alginate immobilized cultures of the thermotolerant yeast, Kluyveromyces marxianus IMB3, on glucose-containing media at 45 degrees C, it was found that initial yields produced by the immobilized culture lagged behind those produced by cultures in free suspension. However, in subsequent batch-feed experiments it was demonstrated that the ethanol-producing ability of the immobilized preparation increased with successive feeds, while production by the free suspension reduced significantly.