Observations were carried out for 22 months on 1142 tonnes of wheat stored in a metal bin equipped with an aeration system and a fan withdrawing air at a rate of 5150 ft 3/min. The observations comprised temperature measurements of the grain bulk, records of the ambient temperature and humidity and of the hours of fan operation, and examination of grain condition as indicated by moisture content, germination, insect infestation, and the percentage of damaged grains. The observations showed that during the first year beginning in May 1966, 1212 hr of aeration lowered the temperature of different layers of the grain bulk from averages of 26·8–32·2°C to 10·2–13·8°C. During the summer of the second year the grain temperature rose to averages of 18·1–19·2°C. During the second winter of storage, 523 aeration hr cooled the grain bulk to averages of 10·5–14·3°C. The grain remained in excellent condition throughout the almost 2 years storage period.