350 cases radiographed in Georgetown, British Guiana, were diagnosed on the basis of a typical clinical picture, a blood eosinophilia of at least 2,500/mm3, characteristic changes on a chest film and a rapid response to treatment. Tropical eosinophilia, formerly considered a syndrome, is now known to be a disease of filarial aetiology. Radiological appearances were described as normal in 2 per cent, “basic pattern” in 62 per cent and “basic pattern plus” in 36 per cent. Where possible, radiographic detail was related to pathology. The diagnostic value of chest films was discussed and the constancy of the X-ray change stressed against the fluctuation of the clinical and haematological picture. Highly satisfactory clinical results of treatment contrast with the less adequate radiological response. The group of conditions combining lung change and blood eosinophilia was surveyed. Radiological differential diagnostic principles and their application were given. Tropical eosinophilia may recur in temperate cli...