SUMMARYThe influence of 3 temperatures and 6 relative humidities upon the growth and survival of ten fungi isolated from moldy silages was studied. The fungi wereAlternaria tenuis, Aspergillus fumigatus, Chlamydomyces palmarum, Cladosporium elatum, Fusarium moniliforme, Monascus purpureus, Mucor jansseni, Mucor racemosus, Geotrichum candidum, andPenicillium purpurogenum.No growth was observed at 50°C, but all developed at 25°and 37°in atmospheres above 85 per cent relative humidity on soybean ensilage. Maximum growth occurred at 25°and 100 per cent relative humidity, with a gradual reduction as the relative humidities were lowered. A sharp decline was noted below 80 per cent relative humidity.Aspergillus fumigatusandMonascus purpureuswere the only fungi able to grow at 65 per cent relative humidity. The inoculum ofA. fumigatus, M. purpureus, andPenicillium purpurogenumsurvived 30 days exposure to 50°at high humidities. None of the other fungi survived the exposure.