A series of 4-oxo-4H-pyrido[1,2-a]thieno[2,3-d]pyrimidines with substitutions in the 2, 3, and 7 positions was prepared. The compounds were evaluated in the rat passive cutaneous anaphylaxis test for antiallergy activity. Several compounds had potent oral activity and were found to be superior to disodium cromoglycate and doxantrazole. Structure-activity relationships are discussed.