The triplet excited states of (S)- and (R)-flurbiprofen (FBP) have been used as reporters for the microenvironments experienced within the binding sites of human and bovine serum albumins. Regression analysis of triplet decay provides valuable information on the degree of protection that these excited states are afforded from attack by a second FBP molecule, oxygen, or other reagents. The multiexponential fitting of these decays can be satisfactorily correlated with the distribution of the drug among the two binding sites and its presence as the noncomplexed form in the bulk solution. This assignment has been confirmed by using (S)-ibuprofen or capric acid as selective site II replacement probes. Triplet lifetimes and site occupancy are sensitive to the type of serum albumin employed (human versus bovine). Finally, the binding behaviour of (S)- and (R)-FBP exhibits little stereoselectivity.