Lymph nodes from cats with natural feline immunodeficiency virus (FIV) infection were examined histopathologically for characterization of lesions in the symptomatic and terminal stages. The localization of viral antigen was also studied in the nodes by immunohistochemistry using a monoclonal antibody to FIV p24. In a node of persistent generalized lymphadenopathy stage, follicular hyperplasia was prominent and the viral antigen was demonstrated predominantly in the follicular lymphocytes and tingible body macrophages. In cats died at AIDS related complex stage, the lymph nodes showed either mixed follicular hyperplasia and involution, involution, or mixed involution and depletion. The lymph nodes in those died at AIDS stage showed considerable destruction of the nodal architecture with involution and depletion of lymphoid follicles. In this terminal stage, the viral antigen was seen prominently in histiocytes/macrophages of the sinus. These findings observed in the dead cats were similar to the lymph node changes seen in human AIDS associated with HIV infection. It was suggested that sequential histologic changes from follicular hyperplasia to depletion via involution took place in the FIV infected lymph node with persistence of FIV antigen.