The effects of storage condition on the shelf life of the AIN-76 diet were investigated. Samples of the diet were stored at -70 degrees, 4 degrees, 20 degrees, and 23-30 degrees under atmospheric air and at 4 degrees and 20 degrees under argon. Levels of vitamin A, thiamine, rancidity, bacteria and mold were monitored during 168 days of storage. A 41.3% loss of vitamin A occurred in samples stored at 23-30 degrees. A marked decline in thiamine was observed in all samples stored at 20 degrees or above. Loss of thiamine was significantly greater in samples stored at 20 degrees than in those stored at 4 degrees, and greater in samples stored under air than those stored under argon. Rancidity reached a level previously shown to be associated with a disagreeable odor and taste (peroxide value greater than 140) with in 30, 50 and 90 days when the diet was stored at 23-30 degrees or 20 degrees under air and 20 degrees under argon, respectively. Peroxide values remained well below 140 in samples stored at 4 degrees or colder. None of the nutritional parameters tested reached unacceptable levels in any of the samples stored at 4 degrees or colder during the 168 days. These results indicate that to achieve maximum shelf life, the AIN-76 diet should be stored at 4 degrees or colder. Although less effective than low temperature, an argon atmosphere extended the shelf life and was additive with lower temperatures.