Ergosterol, the principle sterol of many wild-typeNeurosporaand other Ascomycetes, had a greater affinity for polyene antibiotics than did lichesterol or eburicol, the sterols of some resistant mutant strains. The affinity was demonstrated by comparing the sterols extracted from sensitive and resistant strains ofNeurospora crassaandCandida albicansfor protection against polyene inhibition of sensitiveN.crassaand for their ability to alter specific polyene absorption maxima.