Intradermal 13-hydroxyoctadecadienoic acid (13-HODE; 10(-11)-10(-9) mol/site) inhibited oedema formation induced by the neutrophil-dependent mediator leukotriene B4 (LTB4) in the presence of calcitonin gene-related peptide (CGRP; 10(-11) mol/site) in rabbit skin. In contrast, the responses to the direct acting mediators bradykinin and histamine were unaffected by 13-HODE. 13-HODE failed to induce oedema formation in rabbit skin when injected alone or in the presence of the potent vasodilator CGRP. These results present a novel interaction between 13-HODE and LTB4 that could have important implications in the pathogenesis of inflammation.