The metabolism of arachidonic acid, by isolated peritoneal macrophages in response to stimulation with microorganisms isolated from continuous ambulatory peritoneal dialysis (CAPD) patients, is not specific to the individual strain but is determined by species. Isolates of Staphylococcus aureus (n = 7) and Staphylococcus epidermidis (n = 13) produced a significant increase in leukotriene B4 generation by peritoneal macrophages compared with unstimulated cells (P less than .001). The coincubation of peritoneal macrophages with gram-negative organisms (n = 3), however, did not result in an increase in leukotriene B4 synthesis. In contrast, all the organisms tested significantly inhibited the formation of prostaglandin E2 and thromboxane B2 but the degree of inhibition was species dependent. The above results were reproduced using bacteria-free supernatants, indicating that the interaction was dependent on a secreted bacterial product. Thus in response to certain bacterial species, the recruitment of neutrophils may be facilitated by the generation of leukotriene B4 from peritoneal macrophages. In addition, the reduction in synthesis of prostaglandin E2 may remove a regulatory effect that this metabolite has on the immune response.