A new simple concept for a miniaturized monolayer trough is described. The overall monolayer area in the expanded state is approx. 150 mm2 and can be reduced by a factor of 2. The surface area is a function of the shape of the meniscus formed by the subphase and is controlled by the amt. of water in the monolayer trough. The controlled compression of monolayers to a desired area per mol. with simultaneous observation of the lateral distribution of fluorescently labeled mols. is shown. A biol. reaction between a specific antibody and lipid anchored peptide demonstrates the feasibility of monolayer expts., which require only very small quantities of substance (in the pmol range). This trough might also be a valuable tool for the 2D crystn. of proteins at lipid layers via specific binding sites such as metal chelators. [on SciFinder (R)]