Drug binding to humanserumalbumin (HSA) has been characterized by a spin‐labeling and continuous‐wave (CW) EPR spectroscopic approach. Specifically, the contribution of functional groups (FGs) in a compound on its albumin‐binding capabilities is quantitatively described. Molecules from different drug classes are labeled with EPR‐active nitroxide radicals (spin‐labeled pharmaceuticals (SLPs)) and