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The correspondents are correct in doubting my doubts about aminopterin and thalidomide effects on the brain. Aminopterin can cause malformations of the brain in human embryos as shown by Thiersch (Acta Endocrinol, suppl 28:37, 1956) and thalidomide has been held responsible for damage to the central nervous system (Horstmann W, Z Kinderheilkd 96:291, 1966) in some children.