The role of epistatic interaction of allozymes in the determination of variation in larval ethanol tolerance of Drosophila melanogaster was examined. Isofemale lines from the Tahbilk Winery were made homozygous for different common alleles of alcohol dehydrogenase (Adh) and sn-glycerol-3-phosphate dehydrogenase (Gpdh). When fed 6% ethanol, all the lines had reduced survival and, in the survivors, reduced body weight and lengthened development time. A strong positive correlation between tolerance and development time suggested that alleles responsible for slowing development on ethanol also increased ethanol tolerance. Analysis of larval ethanol tolerance over four generations showed that larvae of the AdhffGpdhff, and AdhssGpdhss allelic combinations were more tolerant than larvae with the other combinations. However, these genotypes were not associated with the slowing of development nor the weight loss on ethanol. Hence, larvae with certain combinations of Adh and Gpdh allozymes may have a greater capacity to metabolize ethanol and be more tolerant to its toxic effects.