Abstract: There are provided 4-benzyl-1-(2H)-phthalazinone derivatives having antiallergic activity of the formula ##STR1## wherein R.sub.1 represents fluorine, chlorine, bromine, trifluoromethyl, C.sub.1 -C.sub.6 -alkyl, hydroxy, C.sub.1 -C.sub.6 -alkoxy, C.sub.2 -C.sub.6 -alkanoyloxy, amino, C.sub.1 -C.sub.6 -alkylamino, di-C.sub.1 -C.sub.6 -alkylamino, C.sub.2 -C.sub.6 -alkanoylamino, C.sub.2 -C.sub.6 -alkanoyl-C.sub.1 -C.sub.6 -alkylamino or a nitro group, R.sub.2 represents hydrogen or has one of the meanings given for R.sub.1, whereby R.sub.1 and R.sub.2 may be the same or different, the radicals R.sub.3 and R.sub.4 are the same or different and represent hydrogen, halogen, C.sub.1 -C.sub.6 -alkyl, hydroxy, C.sub.1 -C.sub.6 -alkoxy, benzyloxy or C.sub.2 -C.sub.6 -alkanoyloxy and A represents an azacycloalkanyl radical, the aza nitrogen of which contains a C.sub.1 -C.sub.6 -alkyl group which is substituted by various radicals, and processes for their manufacture.