The peptido-leukotriene receptor(s) (PL) on the ferret isolated spleen strip have been characterised by functional studies using the naturally occurring leukotrienes (LTs), a range of structurally distinct PL antagonists, and by ligand binding studies. LTB4 (0.01-10 microM) was inactive on ferret spleen whereas LTC4, LTD4 and LTE4 produced concentration-related contractions with maximal responses, relative to noradrenaline, of 57% (EC50 0.28 microM), 60% (EC50 0.5 microM) and 7% respectively. The leukotriene responses were unaltered by L-serine borate, L-cysteine, indomethacin, phentolamine, propranolol, mepyramine, methysergide or atropine, suggesting that the peptido-leukotrienes were acting through distinct PL receptors. The PL1 antagonists, FPL 55712 (0.01-10 microM), ICI 198615 (10 microM), SK&F 104353 (10 microM) and MK541 (10 microM) were all inactive against LTC4- or LTD4-induced contractile responses. LTE4 was a partial agonist with respect to LTC4 and LTD4 with pKB values of 5.8 and 5.5 respectively. Nifedipine (0.1 microM) produced a rightward shift of the concentration-response curves to both LTC4 and LTD4 and depressed their maximal responses. An unacceptably high level of non-specific binding of [3H]LTD4 to membrane preparations of ferret spleen prevented characterisation of this receptor by ligand binding. These results suggest that the ferret spleen has a homogeneous population of a PL receptor type which is insensitive to existing PL1 receptor antagonists. The functional characteristics of this PL receptor type are similar to those of the PL2 receptor on other tissues. The absence of PL1 receptors on this tissue makes it particularly useful in identifying new and selective drug tools for the PL2 receptor.