With increasing use of proteins in many different applications, ranging from phramaceuticals to biosensors and biomaterials, there has emerged a need for protein structural characterisation in diverse environments. In many cases it is not sufficient to just have the three-dimensional structure of a protein in H2O or in the crystalline state. Often information on the structural properties of a protein is required in the presence of organic solvents, detergent micelles, phospholipid membranes and so on. Fourier transform infrared spectroscopy (FTIR) has been identified as one of the few techniques that can be applied for structural characterisation of proteins in such environments. Here we discuss how this technique is being used to obtain information on protein structure and stability in both aqueous and non-aqueous media. Examples are drawn from our studies of water soluble proteins and membrane proteins. (C) 1999 Elsevier Science B.V. All rights reserved.