2,4-Diamino-5-benzylpyrimidines characterized by the formula ##SPC1## Wherein R.sup.1, R.sup.2, A.sup.1, Z and n are as hereinafter set forth, are described. The 2,4-diamino-5-benzylpyrimidines of the invention have useful antibacterial activity. More particularly, they block bacterial dihydrofolate reductase and potentiate the antibacterial activity of sulfonamides.