1. During studies of the role of platelet-activating factor (PAF) in macrophage superoxide anion generation (O2(-1], we identified an agonist action of the putative PAF receptor antagonist 1-O-hexadecyl-2-acetyl-sn-glycero-3-phospho (N,N,N-trimethyl) hexanolamine (hexanolamine PAF) in guinea-pig macrophages. The 1-O-octadecyl form of this compound has specific antagonist actions at PAF receptors. 2. The agonist properties of hexanolamine PAF were examined in rabbit washed platelets (aggregation) and in guinea-pig peritoneal macrophages (O2- generation). 3. Hexanolamine PAF induced significant platelet aggregation (50% of the PAF maximum). However, the omission of bovine serum albumin (BSA) from the Tyrode buffer resulted in a diminution of the response of washed platelets during storage for 24 h at 4 degrees C (7% of PAF maximum), whereas the maximum response to PAF was unaffected by storage for this period, irrespective of the presence of BSA. 4. Platelet aggregation induced by hexanolamine PAF was not accompanied by a detectable increase in intracellular calcium [Ca2+]i, whereas the aggregation response to PAF was preceded by a large rise in [Ca2+]i. 5. Hexanolamine PAF induced O2- generation in adherent macrophages, with a maximum response 45% of that to PAF. Hexanolamine PAF (100 nM), at a concentration equi-effective with PAF (1 nM) for stimulation of O2- generation in macrophages, induced an increase in [Ca2+]i which was significantly less than that induced by PAF. 6. PAF concentration-response curves were constructed in platelets or macrophages following pretreatment with hexanolamine PAF (0.1 and 1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)