Rainbow trout macrophages maintained in short term culture when incubated with either calcium ionophore, A23187, or opsonized zymosan synthesize a range of lipoxygenase products including lipoxins and leukotrienes. These cells are unusual in that they generate more lipoxin than leukotriene following such challenge. The main lipoxin synthesized was lipoxin (LX) A4. This compound was identified by cochromatography with authentic standard during reversephase high performance liquid chromatography, by ultra violet spectral analysis, radiolabeling following incorporation of [14C]arachidonic acid substrate into macrophage phospholipids, and gas chromatography electron impact mass spectrometry of the methyl ester, trimethylsilyl ether derivative. Other 4-series lipoxins synthesized by trout macrophages were identified as 11-trans-LXA4, 7-cis-11-trans-LXA4, and 6(S)-LXA4. These cells also produced 5-series lipoxins tentatively identified as LXA5, 11-trans-LXA5 and possibly 6(S)-LXA5. No LXB4 or LXB5 was, however, detected. The dynamics of leukotriene and lipoxin release were also determined. Lipoxin generation was slower than leukotriene generation the latter reaching a maximum after 30 min of exposure to ionophore (5 microM, 18 degrees C) compared with 45 min for the former.