Solid phase microextraction coupled to high performance liquid chromatography with UV detection (SPME/LC-UV) has been employed to study the binding of delorazepam to human serum albumin (HSA) and bovine serum albumin (BSA). The procedure could also be potentially extended to the measurement of partition coefficients between a wide variety of semi- or non-volatile compounds and matrices. The method is solvent free, simple, fast, and drawbacks of the conventional analytical techniques are avoided. Moreover, the matrix did not interfere with the measurement by binding to the fibre and the amount extracted by the fibre was negligibly small; thus it did not disturb the delorazepam-protein binding.