We report the results of our in vitro experiments on the effects of an L-Arg terminal synthetic hypoxanthine derivative (ST 789) on human neutrophil function. To verify the hypothesis that the reported immunomodulatory effects of ST 789 in vivo are accounted for, at least in part, by effects on phagocytic cells, we experimented in parallel also with methisoprinol, a well known stimulator of neutrophil chemotaxis, structurally related to ST 789. Our results demonstrate that ST 789 is able to improve the true chemotactic response of human neutrophils without interfering with other phagocytic functions, following a pattern largely shared by methisoprinol. Accordingly, ST 789 may be able, when used in vivo, to prime neutrophils for timely and efficient migration to inflammatory sites, and it could be considered for therapeutic use in patients with impaired inflammatory response or severe infections.