Pyrido (1,2-a) pyrimidine derivatives

Pyrido[1,2-a]pyrimidine derivatives of the general formula [I] and their physiologically acceptable salts are provided: <CHEM> where R is a hydrogen atom, a halogen atom or a methyl group, and n is 0, 1 or 2. The pyrido[1,2-a]pyrimidine derivatives and their salts exhibit an excellent antagonistic effect on the slow-reacting substance of anaphylaxis and, therefore, are useable for the treatment of allergic diseases.