A killer toxin-like protein was found in the culture supernatant of a strain isolated from soil. The strain was classified and designated as Streptomyces sp. F-287. The molecular weight of the purified killer toxin-like protein was estimated to be 9,500 by SDS-PAGE. The purified protein was heat stable (100 degrees C, 5 min), pH stable (pH 6.0-9.0, 60 degrees C, for 30 min), and had a relatively wide action spectra. The SKLP showed a cytocidal effect on both budding yeast, Saccharomyces cerevisiae W303 (IC50 = 15.6 micrograms/ml) and on fission yeast, Schizosaccharomyces pombe SP870 (IC50 = 20.0 micrograms/ml). The SKLP also caused morphological changes on some sensitive yeasts and filamentous fungi. These characteristics are apparently different from known killer toxins. These results suggest that this is a novel killer toxin-like protein from Streptomyces sp. strain F-287.