Abstract In the gas chromatographic determination of polycyclic aromatic compounds (PACs), internal standards (I.S.s) are frequently used in order to correct for losses and fluctuating experimental variables. It is shown that fluorinated PACs exhibit many advantages as I.S.s. Thus, for each parent compound, several standards can be obtained, which means that the optimum I.S. can be selected for each sample so as to avoid co-elution with other sample components. Another advantage is the possibility of adding I.S.s to the sample during different stages of the work-up with the result that the associated losses in each step can be measured in one determination. This work centred on fluorinated naphthalenes, biphenyls and phenanthrenes. Samples included a coal tar (SRM 1597) and a chimney ash.