A gas chromatographic-mass spectrometric (GC-MS) study of the polycyclic aromatic hydrocarbon (PAH) composition of a series of 72 marine sediments collected from the Guipuzcoan Coast (Bay of Biscay, Spain) showed three end-member distributions, one related to pyrolytic soot contributions (type A), another to combined paper mill effluents and soot inputs (type B) and the third to petrogenic residues (type C). The detailed composition of each of these end-member mixtures is given. Further examination of the PAH extracts by GC-negative ion chemical ionization MS illustrated several previously unreported selectivity effects such as enhancement of the parent PAHs eluting with longer retention times and the increased response factor of the alkyl homologues corresponding to the m/z 252, 276 and 302 hydrocarbons.