Serum albumins (SA) are important proteins very abundant in the organism. Their main physiological function is to carry different endogenous and exogenous agents (including drugs) through the blood-stream. Binding of drugs to SA in biological systems is a key process that can modulate a number of properties of the carried agent, such as increased solubility in plasma, decreased toxicity, etc; hence, binding is essential for understanding biodistribution, metabolism, elimination or pharmacological effect of drugs in the body. In this context, the transient species of drugs generated by irradiation were used as probes to study the drug-SA interactions, as their properties are quantitative parameters sensitive to the microenvironment.