[en] As bovine serum albumin (BSA) undergoes acid- or base-induced conformational changes, the binding of benzo(a)pyrene (BaP) to BSA, as well as the type II uv fluorescence (380 nm) due to pyrene-like oxidation products, increases. The presence of fatty acids also enhances the binding of BaP to BSA at neutral pH, whereas the visible fluorescence of BaP is effectively quenched by fatty acids. L-Tryptophan, which is specifically bound to BSA, enhances the BaP binding and particularly the formation of pyrene-type products. Upon removal of oxygen, the production of the type I uv fluorescence (340, 357, 378 nm) probably due to BaP radicals is diminished and hydroxy-BaP derivatives are not formed. While BaP undergoes oxygen-dependent reactions with cysteine, non-carcinogenic benzo(e)pyrene does not react with cysteine. The BaP fluorescence of young collagen (from 4 to 6 weeks old rat tail tendon) is more intense than that of old collagen (from about 2 years old rat tail tendon). With increasing temperature, the former fluorescence decreases, whereas the latter increases. The denaturation temperature of both BaP-collagen and uv (365 nm)-irradiated BaP-collagen complexes does not differ from that of collagen itself