Novel pteridines of formula (I), ##SPC1## wherein R is an optionally substituted phenoxyalkyl group, and R.sup.1 and R.sup.2 are the same or different and each is a lower alkyl group or R.sup.1 and R.sup.2, together with the carbon atom in the pteridine ring structure, form a spirocycloalkyl ring system having 4 to 6 carbon atoms outside the pteridine ring structure, And their method of preparation. The above compounds have bacteriostatic activity.