Pollution has been assessed as a mutagenic activity determined by the Ames test, using radiolabelled benzo[a]pyrene (BaP) as a model pollutant. Experimental animals were sponges, mainly Tethya lyncurium from the Northern Adriatic and from the Pacific near Catalina Island, California, U.S.A. Changes in ornithine decarboxylase (ODC) activity (ODC; EC 4.1.1.17) and polyamine concentrations with and without pollution were observed. There is a slow rise in ODC activity during the course of three-weeks exposure and a fast increase of polyamine levels during the course of one day. Mixed function oxygenase (MFO; EC 1.14) activity could not be detected in sponges. There was a significant concentration dependent coupling of radioactive BaP derivatives (BaPD) to the macromolecular fractions; the highest in protein, X 1000 greater than DNA and X 500 greater than RNA. Coupling is light-mediated and drops to zero in the dark. However when activated microsomal fractions from fish, that had been exposed to high level polycyclic aromatic hydrocarbon (PAH) pollution are added, dark incorporation rises to significant levels which can be decreased by the MFO inhibitor 7,8-benzoflavone (BP). The question of possible absence of DNA repair in the sponges and some implications are discussed.