The effects of hybrid and mechanical damage on equilibrium relative humidity (ERH) and allowable storage time (AST), as determined by CO2 production and dry matter loss caused by fungi, were measured for shelled corn. The results were used to study the relationship between ERH and AST. Corn with 16% mechanical damage had lower ERH than corn with 2% mechanical damage, but corn with greater mechanical damage had shorter AST. Normally, fungi grow more slowly (meaning AST is longer) at lower ERH. Apparently, the seed pericarp breakage associated with mechanical damage allowed faster fungal growth even though mechanical damage reduced ERH. Pioneer hybrid P3377 had higher ERH and shorter AST than hybrids FRB73仗o17 and FR35乏R20. Differences in ERH helped explain the differences in storability of the hybrids. For 13 to 22% moisture corn, chemical composition could be used to predict the ERH of each hybrid within two percentage points, and thus composition could be used to predict the relative storability of each hybrid.