Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to counteract stress hormone and pro-inflammatory cytokine activation. To extend these findings, we tested whether the NSAID diclofenac sodium would attenuate lipopolysaccharide (LPS)-induced reductions in reward behavior. In the first experiment, male, Wistar rats pressed a lever for food reward and subsequently received 10 days treatment of saline (1 ml/kg, s.c.) or diclofenac (2.5mg/kg, s.c.). On the subsequent test day, rats were given a final injection of saline or diclofenac 30 min prior to LPS (20 micrograms/kg, i.p.). LPS significantly reduced rate of food self-administration and total reinforcers obtained and increased corticosterone levels in saline-treated rats, while these effects were significantly attenuated in diclofenac-treated rats. In the second experiment, rats pressed a lever for sweetened milk. In contrast to food self-administration, acute LPS exposure did not reduce rate of responding or total reinforcers obtained in either saline- or diclofenac-treated rats. In the third experiment, rats trained to press a lever for sweetened milk were pre-exposed to a high dose of LPS (250 micrograms/kg, i.p.) 2 weeks prior to a challenge injection of LPS. In this case, LPS challenge significantly reduced rate of sweetened milk self-administration, but not total reinforcers obtained, in saline-treated rats. Rats treated with diclofenac did not exhibit reductions in rate of responding or total reinforcers obtained. Overall, the data indicate that the NSAID diclofenac sodium counteracts LPS-induced reductions in reward behavior and corticosterone release, and may therefore have therapeutic potential for specific components of endotoxin-induced sickness behavior, including anhedonia.