in lipoxygenase products from synovial fluid in carragheenan-induced arthritis in dogs. APMIS 96: 60 1-604, 1988.A non-suppurative chronic arthritis was induced in the juvenile dog knee by intra-articular instillations with Carragheenan. Lipoxygenase products of arachidonic acid were separated from synovial fluid by reversedphase high-performance liquid chromatography (RP-HPLC). After ten weeks we observed an accumulation of leukotriene B, (LTB,) in synovial fluid in five out of six experimental knees (0.94 to 5.5 ng/ml), as judged by integrated optical density. Biological activity of LTB, was confirmed by chemokinesis. LTB, was not detected in control knees. The 1 5-lipoxygenase products, 1 5-hydroxyeicosatetraenoic acid ( 1 5-HETE) and 13-hydroxy-9,lI -0ctadecadienoic acid (1 3-HODD), being inhibitors of 5-lipoxygenase, were found in relatively high levels in the control knees compared to the arthritic knees. The results denote LTB, as a pro-inflammatory local mediator during carragheenan-induced arthritis; possibly, the decreased levels of 15-HETE and 13-HODD in the arthritic knees may have a regulatory function, thus facilitating LTB, generation.