In conjunction with studies of the rodent populations of the former nuclear test site at Eniwetok Atoll, the feeding patterns of Rattus rattus and Rattus exulans were determined by food acceptance tests, histological examination of stomach contents, and observation of animals under both natural and cage conditions. Both species were active in all community types from the early successional stages to the shrub-tree stage. R. exulans was found mainly on islets having the remnants of coconut plantations, whereas R. rattus occurred on those extensively disturbed by nuclear testing. Plant foods predominated in the diets of both species; however, R. rattus used a wider range of foods, including a variety of insects. The apparent narrower preferences of R. exulans might explain its absence from islets that suffered habitat destruction and restriction of food sources during the nuclear test program.