Interleukin-1 (IL-1) is a proinflammatory cytokine, alpha-MSH(1-13) molecules inhibit inflammation induced by cytokines, other mediators of inflammation, and by peripheral irritants. D-valine substitution in the antiinflammatory/antipyretic message sequence [alpha-MSH(11-13), Lys-Pro-Val] of alpha-MSH(1-13) increases the activity of the tripeptide. Our aim was to learn if D-valine substitution also enhances the antiinflammatory activity of the entire alpha-MSH(1-13) molecule and to determine if an antipyretic D-valine-substituted alpha-MSH(8-13) molecule is also antiinflammatory. Intraperitoneal injection of alpha-MSH(1-13) and of (D-Val13)alpha-MSH(1-13) caused dose-related suppression of ear edema induced in mice by intradermal injection of IL-1 beta; the two molecules were equipotent. (D-Val13)alpha-MSH(8-13) likewise inhibited inflammation, but the potency was less than that of the larger molecules. Intracerebroventricular injections of (D-Val13)alpha-MSH(1-13) and of the unsubstituted molecule were equipotent in reducing inflammation; the (D-Val13)alpha-MSH(8-13) molecule was less effective. The results support the idea that the alpha-MSH(1-13) molecule inhibits inflammation and suggest that the L-conformation of alpha-MSH(1-13) is maximally effective with regard to its antiinflammatory activity. The results with alpha-MSH(8-13) are consistent with previous findings of lesser antihost response activity of alpha-MSH fragments that contain the COOH-terminal tripeptide Lys-Pro-Val.