In this paper we have described the binding of nanomoler concentrations of [3H]leukotriene B4 (LTB4) to human polymorphonuclear leukocytes. Because up to 80% of the total [3H]LTB4 binding was blocked by excess (greater than 100 times) [14C]LTB4, the majority of binding is specific. Stereospecificity of the LTB4 binding is demonstrated by the diminished relative abilities of the 6-trans-and 12-epi-6-trans- isomers of LTB4 to block [3H]LTB4 binding. With these two isomers 3-10-fold higher than [14C]LTB4 concentrations were needed for equivalent inhibition of [3H]LTB4 binding. This difference is quantitatively less dramatic than the differences between these isomers in many in vitro functional assays such as chemokinesis, chemotaxis, and degranulation. Binding of [3H]FMLP is not blocked at greater than 100-fold excess of LTB4. The binding of [3H]LTB4 to cells appears to be essentially irreversible at 4 degrees C, but not at 37 degrees C where initially bound LTB4 is rapidly converted to metabolites which then enter the medium. These results suggest the presence of a saturable, stereospecific site for LTB4 on PMN. The association of LTB4 binding and the initiation of pharmacological responses to LTB4 will require further studies.