Human polymorphonuclear (PMN) leucocytes bind synthetic [3H]-labelled leukotriene C4 ([3H]LTC4) with rapid saturation and reversibility of approximately 90%, by a 700-fold higher concentration of non-radioactive LTC4. [3H]LTC4 is recognized specifically by 10,778 +/- 6260 (mean +/- SD) sites per PMN leucocyte that exhibit a KD of 34.3 +/- 1.7 nM. The specificity of the LTC4 receptors is supported by the competitive inhibition of binding of [3H]LTC4 by LTC4, LTC4-sulphone, LTD4, and LTE4 with relative potencies of approximately 100:20:3:1. The four-fold higher level of specific binding of [3H]LTC4 by sonicates than by intact PMN leucocytes is attributable to intracellular receptors. Of the total number of receptors recovered in sonicates of PMN leucocytes, one-third are associated with membranes and the other two-thirds with lysosomal granules. The affinity of the membrane receptors for LTC4 is indistinguishable from that of receptors on intact PMN leucocytes, whereas the affinity of granule receptors is significantly higher. The characteristics of the receptors are consistent with a role in mediating uptake and metabolism of LTC4 by PMN leucocytes.