To the Editor.— I have discovered thermophilic actinomycetes ( Thermoactinomyces ) growing in 66% of frost-free home refrigerators surveyed. Samples were taken from the drip pans of 230 refrigerators from homes in Indiana, New Jersey, and Illinois. Thermoactinomyces , which is a known cause of hypersensitivity pneumonitis (farmer's lung), readily produces millions of spores during growth. More recently, I have isolated Thermoactinomyces from warm moist dirt at the outside bottom of a home freezer. Previously, Thermoactinomyces was found by others in overheated hay, grain, and bagasse, as well as in home heating systems and humidifiers. I suggest cleaning the drip pan with detergent once a month.