The therapeutic effect of oxatomide on experimental otitis media with effusion (OME) induced by secondary immune response was investigated in chinchillas. Oxatomide was administered daily in three different doses (5, 10, 30 mg/kg b.w.t.) for a period of 2 weeks, starting 2 days after the instillation of keyhole limpet hemocyanin (KLH) into the tympanic cavity. The severity of OME was assessed by observing the eardrum under a surgical microscope, by tympanography, and by histological findings. The concentrations of leukotriene C4 and LTD4 in middle ear effusion (MEE) were also measured, 7 days after the KLH instillation. It was found that oral administration of oxatomide in dosages of 10 and 30 mg/kg alleviated the experimental OME. The mean LTD4 concentration measured in MEE from chinchillas given 30 mg oxatomide was significantly lower than that measured in the control group. The radioactivity of 14C-labelled oxatomide in MEE and the autoradiographic findings revealed that orally administered oxatomide was rapidly absorbed from the digestive tract and transported to the middle ear via blood circulation. The findings suggest that the effect of oxatomide can be anticipated in patients with OME.