The ability of organisms, or individual cells to sense and to react to different external and internal stimuli (light, hormones, odorants, taste) is crucial for their survival. I will report on our recent progress to investigate mol. signal recognition and transduction processes by a combination of surface sensitive phys. techiques and mol. biol. methods. Controlled self-assembly of proteins in a functionally active form on sensor surfaces is a prerequisite for investigating mol. interactions by surface-sensitive techniques. Here, receptors are reversibly immobilized on solid supports; ligand binding to and concomitant conformational changes of the receptors are probed by optical techniques (total internal reflection fluorescence and IR spectroscopy, fluorescence correlation spectroscopy and surface plasmon microscopy). In addn., we have developed a method to detect channel gating of ionotropic receptors in tethered membranes on planar solid surfaces. As an alternative to traditional patch clamp measurements, this approach offers novel possibilities for an efficient screening of receptor function. [on SciFinder (R)]