The analysis of protein-protein interactions plays an important role in understanding many biological processes. Microscale Thermophoresis (MST) permits a robust and fast analysis of protein-protein interactions even in highly complex biological liquids. Here we have investigated the binding of TEM1 β – Lactamase to BLIP (β – Lactamase Inhibitory Protein) using Microscale Thermophoresis. The experiments were performed as in 50% mammalian cell lysate, as well as in standard buffer. The TEM1-BLIP system is very well characterized by various biophysical methods, such as Surface Plasmon Resonance (SPR).The role of residue substitutions at the interface of the proteins was easily studied using TEM1 and BLIP mutants. Dissociation constants (Kd) determined for TEM1 and BLIP show an excellent agreement with previously published data.