Plasma from seventeen children with arthritis was investigated for the content of lipoxygenase products. Two of the patients had untreated juvenile chronic arthritis, three had a pyogenic joint infection, four had Henoch-Schonlein purpura and eight had reactive arthropathy. After lipid extraction, the lipoxygenase products were identified by high-performance liquid chromatography (HPLC). Chemotactic material coeluting with leukotriene B4 (LTB4) was found in plasma from the arthritis patients. Enhanced chemotactic activity of this compound was found in juvenile chronic arthritis and pyogenic arthritis patients, compared to the chemotactic activity in plasma from patients with Henoch-Schonlein purpura and reactive arthropathy. The findings may indicate that activation of lipoxygenases may play a role during the initiation of the inflammatory reaction in arthritis.