Interactions between serum albumins (HSA, human, and BSA, bovine) and fluoroquinolones (FQs), such as enoxacin, norfloxacin, ciprofloxacin, and ofloxacin, have been studied using the laser flash photolysis technique. Lifetimes and quantum yields of FQs triplet excited states ((3)FQs) are not affected by the presence of albumins, however, the quenching of (3)FQs by tryptophan and tyrosine and the subsequent generation of FQs. radical anions and tyrosyl or tryptophanyl radicals were detected. These results, besides agreeing with association constants (K-a) for FQs binding to albumins lower than 6 x 10(2) M-1, are highly relevant to understanding the process of photohapten formation, the first event in the onset of photoallergy. The emission of tryptophan within albumin is not affected by the presence of FQs when the inner filter effects (IFE) of these drugs are taken into account, which explains the discrepancies reported in the literature about K-a of FQs with albumins.