Ethanol production by both free and calcium alginate immobilized preparations of the thermotolerant yeast strain K. marrianus IMB3 at 45 degrees C during growth on sucrose-containing media was compared. At early stages in fermentation, concentrations of ethanol produced by both preparations were similar although at later stages in fermentation production decreased less rapidly in the immobilized system. Maximum yields from both systems approximated 88% of the maximum theoretical yield when 4% (w/v) sucrose was used as the carbon source. When both preparations were used for prolonged periods of time (22 days) bl a batch-fed system the yield obtained using the free preparation reduced significantly to 59% of the maximum theoretical yield, whereas that obtained using the immobilized system increased to 98% of the maximum theoretical yield. Copyright (C) 1996 Elsevier Science Ltd.