New 2,4-diaminopyridimidine derivs. have formula (I) In the formula, R is H, CH3 or C2H5; X is 1-10C alkylene; Y is O, S or a direct bond; and Ar is aryl. (I) can be used for the treatment of malaria and/or bacterial infections. Absorption after oral is good, and (I) are active against malaria infections which are resistant to other antimalarials. Specific cpds. (I) include 2,4-diamino-6-methyl-5-(4-chloro-2-cyclohexylphenoxypropoxy)-pyri- midine. In an example, this is prepd. from 2,4-diamino-6-methyl-5-hydroxypyrimidine dihydrochloride and 4-chloro-2-cyclohexylphenoxypropyl bromide.