In the present study serum immuno-inhibitory factors in children with otitis media with effusion (OME) were evaluated. The study included 23 children with OME and 23 healthy age-and-sex-matched controls. Serum inhibitory activity (SIA) was expressed as the inhibition index of proliferative response to T-cells lectins. In almost all the children with OME the indices reflecting T-cell proliferation were below the range of those in the control group. The results suggest that the activity of the factor(s) which affect T-cell proliferation may be included in mechanisms contributing to the persistence of OME in children. Further studies are needed in order to establish the cellular and molecular aspects of serum inhibitory activity, as well as its significance in the pathogenesis of OME.