Precision food pellets made from purified ingredients by two different manufacturers (P. J. Noyes Company, Inc. and Bio-Serv, Inc.), and advertised as dust-free and nutritionally complete, were compared as reinforcers of leverpressing in rats. Single schedules (a variable interval [VI] of 30 sec and a fixed ratio of 20) were used to compare ability to maintain moderate and high response rates, and concurrent VI schedules were used to assess preference. The two pellets maintained equivalent moderate and high response rates on the single schedules. In the concurrent schedules, 3 out of 4 rats showed a small preference for the Bio-Serv pellets. Although both pellets performed adequately in normal humidity, high humidity caused the Bio-Serv pellets to soften and occasionally to be crushed in the pellet dispenser. Their softness may have been the reason they were preferred. The two pellets can be regarded as generally equivalent, except in high humidity. The only experiments in which they might not be used interchangeably are those involving choices between different reinforcers.