At least four distinctive sterol functions have been defined in the yeast Saccharomyces cerevisiae. One of these functions, identified as sparking, has the lowest quantitative requirement for sterol, but has the greatest structural specificity. Based on studies utilizing a yeast strain auxotrophic for both heme and sterol biosynthesis, it had been reported that a delta 5-sterol was essential for the growth of the organism. We demonstrate here that heme, and not a heme precursor, can replace the delta 5-sparking sterol requirement of heme auxotrophic strains of yeast.