We have recently described a new method for analysis of protein interaction on solid surfaces. The basic idea of the method is to make a gradient of chemical groups on the surface and to quantify protein adsorption along the gradient with the use of optical methods such as fluorescence measurements or ellipsometry. We have used the technique for experiments on protein adsorption and exchange, and detergent interaction on wettability gradients made on, e.g., silicon oxide surfaces. Several new observations were made which can not be observed without the use of the gradient method. This contribution is a short review of these obtaineer results and related research problems.