A saframycin-non-producing mutant of Streptomyces lavendulae IFM 1291 was found to produce a new tyrosine-derived indicator SL-1 pigment with anti-dermatophyte activity. This paper describes the isolation, structural elucidation and biological properties of SL-1, especially its antimicrobial activity against dermatophytes. Ten saframycin-non-producers were isolated by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. SL-1 was isolated from the culture broth of mutant strain No. 314-39 via fermentation, extraction with ethyl acetate, silica gel and Sephadex LH-20 column chromatography, and crystallization. Structural elucidation using electron ion mass spectrum (m/z 181, molecular formula C8H7NO4), UV, IR, ¹H NMR, ¹³C NMR spectra, and synthesis verification showed SL-1 is (E)-1,2-dihydroxy-4-(2-nitroethenyl)benzene. Biological properties: SL-1 exhibited moderate inhibitory activity against certain Gram-positive bacteria (e.g., Streptococcus pyogenes, Brucella abortus); it was active against some dermatophytes, with the producer itself sensitive to the pigment; it also showed moderate cytocidal activity against cultured L1210 leukemic cells in vitro (ED50 = 1.0 μg/ml). This is the first report on the isolation of SL-1 pigment from natural sources.