SUMMARYThe combined temperature and relative humidity requirements ofAspergillus nigerwere studied with the following results: The optimum conditions for growth are at a relative humidity near 93 per cent and at a temperature near 40°C.; at 100 per cent relative humidity the optimum temperature is near 30°C. Thus for this species the optimum condition for growth is not at saturation and the optimum temperature changes with different humidities.A general survey of the literature shows that the variability among fungi in their response to temperature and humidity is great, indicating that there is no simple temperature-humidity relationship for fungi.