Inbred Lewis (LEW/N) female rats develop an arthritis in response to Group A streptococcal cell wall peptidoglycanpolysaccharide (SCW) which mimics human rheumatoid arthritis. Histocompatible Fischer (F344/N) rats, on the other hand, do not develop arthritis in response to the same SCW stimulus. To evaluate this difference in inflammatory reactivity between the two strains, the function of the hypothalamic-pituitary-adrenal axis and its ability to modulate the development of the inflammatory response was studied. It has been found that, in contrast to F344/N rats, LEW/N rats had markedly impaired plasma ACTH and corticosterone responses to SCW, recombinant human Interleukin-1 alpha (IL-1 alpha), the serotonin agonist, quipazine, and synthetic rat corticotropin-releasing hormone (CRH). In addition, LEW/N rats compared to F344/N rats had smaller adrenal glands and larger thymuses. Treatment of LEW/N rats with replacement doses of dexamethasone decreased the severity of their SCW-induced arthritis. Conversely, treatment of F344/N rats with the glucocorticoid receptor antagonist, RU 486, or the serotonin (5-HT.sub.2) antagonist, LY53857, was associated with development of severe inflammatory disease, including arthritis, in response to SCW. These findings support the concept that susceptibility of LEW/N rats to SCW arthritis is related to abnormal hypothalamic-pituitary-adrenal (HPA) axis responsiveness to inflammatory and other stress mediators and that resistance of F344/N rats to SCW arthritis is regulated by an intact HPA axis-immune system feedback loop.