The rabbit hydronephrotic kidney (HNK) is a model of renal inflammation characterized by a marked increase in arachidonic acid metabolism which is temporally associated with an inflammatory cell influx into the injured tissue. The HNK exhibits an exaggerated elaboration of eicosanoids ex vivo in response to inflammatory agonists (bradykinin and the chemotactic peptide, n-formyl-methionyl-leucyl-phenylalanine). Essential fatty acid (EFA) deficiency [i.e., deprivation of (n-6) fatty acids] attenuated markedly the ex vivo elaboration of eicosanoids and prevented the enhancement of the microsomal cyclooxygenase and thromboxane synthase activity associated with 3 days of ureter occlusion. In contrast, postobstructive release prevented the ex vivo elaboration of eicosanoids by the HNK. When the HNK was assessed morphologically by electron microscopy, both EFA deficiency and postobstructive release markedly reduced the population of interstitial macrophages normally seen in the HNK. Apparently, EFA deficiency blocked the influx of macrophages whereas postobstructive release resulted in the efflux of macrophages from the HNK. Because EFA deficiency has been shown to inhibit the synthesis of leukotriene B4, a potential chemotaxin, it was hypothesized that EFA deficiency might prevent the influx of macrophages due to an inhibition of leukotriene B4 synthesis. Indeed, EFA deficiency suppressed the synthesis of this eicosanoid in blood whereas prostaglandin E2 and thromboxane A2 production were unaffected. In summary, this study demonstrates that EFA deficiency prevents the influx of macrophages into the HNK and prevents the enhanced arachidonate metabolism which normally occurs after ureter obstruction. A potential role for leukotriene B4 as a chemotactic agent in this model of renal inflammation also is suggested.