The material from 667 lymph nodes, originally suspected of toxoplasmosis, was histologically re-examined, to evaluate criteria for diagnosis and differential diagnosis. The results showed that at least 80% of benign lymph node enlargements containing small groups of epithelioid cells were associated with high titres of Toxoplasma antibodies. Furthermore, 85--95% of the lymph nodes in association with high Toxoplasma antibodies showed the typical histological appearances of toxoplasmosis. The histological diagnosis of toxoplasmosis is thus both fairly specific and sensitive. Other lymph node lesions with small groups of epithelioid cells must be considered in the differential diagnosis. Sarcoidosis and tuberculosis usually have a predominance of distinct large epithelioid cell granulomata. Lymph nodes with sinus histiocytosis showing the formation of small groups of epithelioid cells, do not demonstrate prominent hyperplasia and include sparse germinal centres and were not associated with toxoplasmosis. Lymph nodes with disturbed general structure and small groups of epithelioid cells must be carefully assessed because of the significant possibility of malignancy.