Experimental autoimmune uveoretinitis (EAU) is a well-characterized model of immune-mediated intraocular inflammation. The intraocular infiltrate in EAU consists predominantly of T lymphocytes. The in vivo production of interleukin-2 (IL-2), lymphotoxin and IL-4 by these T cells was investigated by in situ hybridization using cDNA probes to lymphokine mRNA. Localization of lymphokine mRNA was found simultaneous with disease onset in areas of T-cell infiltration. Positive signal was seen over cells in the uveal tract, retina and extraocular region. Less than 10% of the population of T cells defined immunohistochemically had positive localization of mRNA for these lymphokines. The number of positive cells was similar for each of the three probes and increased as the disease progressed. The findings suggest that these lymphokines are produced in vivo in immune-mediated intraocular inflammation and may play a role in the immunopathology seen in these conditions.