This invention provides 2,4-diamino-5-benzylpyrimidines represented by the formula ##STR1## wherein R.sub.1 is H or loweralkyl; R.sub.2 is H, loweralkyl or R.sub.3 CO-- wherein R.sub.3 is H, alkyl, or cycloalkyl-loweralkyl; and X is a halogen; and the acid addition salts thereof. These pyrimidine compounds are useful as antibacterial agents, and as potentiators of the antibacterial activity of sulfonamides.