During a 4-week holiday in Thailand a 13-year-old boy from Germany briefly fell ill with diarrhoea without blood-tinged stools and fever. 5 months later oedematous, reddish swellings occurred, at first on the right upper arm, later over the right side of the chest. Especially at night these swellings were associated with severe local and generalized itching. Bilaterally the axillary lymph-nodes were hard and slightly enlarged. There was a marked eosinophilia of 56%, the white count was 22,700/microliters and the serum level of IgE was raised to 1777 IU/ml. No worm eggs or larvae were found in the stool. Enzyme-linked immunosorbent assay, using larvae of Gnathostoma spinigerum as antigen, demonstrated antibodies against this nematode. Gnathostomiasis having been diagnosed treatment was started with albendazole (200 mg twice daily for 21 days), after which the boy was symptom free. After 2 months the eosinophilia had regressed to 10%, the white cell count was normal and the antibody titre had fallen