1. The pathological changes in the lung, liver and lymph-nodes of typical cases of tropical pulmonary eosinophilia are described. 2. Microfilariae have been demonstrated in the centre of nodules in each of these tissues, suggesting that direct invasion by these organisms is the cause of the lesion in this disease. 3. Cases have been encountered with lymph-node and hepatic, but without lung involvement. The lesions in these cases are similar to those seen in the lung, and microfilariae are present. A plea is made to enlarge the concept of tropical eosinophilia to include such cases, and the same time to restrict it to those in which a filarial infection is proved or suspected. 4. Microfilariae recovered from lymph-nodes have been provisionally identified as W. bancrofti-type, but on the analogy of findings in Malaya, it is suggested that these may be of animal origin and that zoonotic filariasis remains the most likely explanation of tropical eosinophilia. © 1960 Dr. K C Chaudhuri Foundation.