Phenyliodinium (I-.+) and diphenylsulfinium radical cations (II.+) have been generated by flash photolysis (lambda(inc) = 347 nm) of diphenyliodonium ions (I+) and diphenyl(4-phenylthiophenyl)sulfonium ions (II+) in acetonitrile solutions at room temperature. I-.+ and II.+ were found to undergo electron-transfer reactions with benzene derivatives resulting in the formation of radical cations of the aromatic compounds. A study involving 25 compounds including various methyl- and methoxy-benzenes, biphenyl, phenol and cresols revealed that electron transfer is independent of the ionization energy E(i) provided that the rates are encounter-controlled This applies to cases where E(1) does not exceed a critical value: E(i, crit) approximate to 820 kJ mol(-1) (I-.+) and 780 kJ mol(-1) (II.+). Bimolecular rate constants decrease with increasing E(i) in the case of aromatic compounds having ionization energies exceeding the critical values. A Marcus-inverted region was not detected.