There were investigated 22 cases from which the thymic tissue was removed either during surgery for cardiovascular malformations (n = 14), or for myasthenia gravis (n = 8). Histological sections were stained with routine morphologic methods, and immunohistochemistry was performed for cytokeratin, CD20, CD3, and S100 protein. Aspects characteristic for thymus involution were found in 11 cases wi...