Spontaneous phosphate-deregulated mutants were isolated from, Streptomyces hygroscopicus 111-81, a producer of a nonpoly- enic macrolide antibiotic complex. Six of the mutants had stable increased antifungal activity. The activities of the remaining ones were unstable, the same or only slightly higher than that of the initial strain. The most productive mutants had morphological features similar to the parent culture.