The peripheral-type benzodiazepine receptor ligands such as PK 11195 and Ro 5-4864 were found more than twenty years ago in the course of research on neurobiology. These ligands were instrumental in pointing out an involvement of the peripheral-type benzodiazepine receptor (PBR) in apoptosis processes. With in mind an improvement of the solubility of PK 11195 in biological media, we report here improved reaction conditions for ...