Eleven spp. of actinomycetes and 8 of molds were isolated from the surface and interior of mushroom compost during peak heating, utilizing compost-infusion and peptone-glucose agars with aureomycin. The Actinomycetes were Nocardia brasiliensis, Pseudonocardia thermophila, Streptomyces rectus, S. thermoviolaceus subsp. pingens, S. thermovulgaris, S. violaceoruber, Thermoacetinomyces glaucus, T. vulgaris, Thermomonospora curvata, T. fusca and Thermopolyspora polyspora. The optimum temperature for growth was 35-55[degree]; 5 grew at 60[degree]C. The molds were: Aspergillus fumigatus, Chaetomium thermophlle, Humicola griseus var. thermoideus, H. insolens, H. lanuginosus, Mucor pusillus, Stilbella thermophila, and Talaromyces duponti. The optimum for growth was 35-50[degree], most grew slightly or abundantly at 55[degree], none grew at 60[degree]C.