Many common techniques used in biochemical and molecular biology analysis involve the generation of signals by immunological or hybridization detection reactions on membranes or photographic films (e.g. ‘windrose blots’, immunoblots). The possibility to undertake comparative and quantitative evaluation of these signals is a basic requirement in most applications. However, visual inspection of immunological detection by colour reactions or by autoradiography using a photographic film does not usually provide a reliable basis for the quantification and interpretation of results. Thus, there is a need for a reproducible, (semi-)quantitative method with an option for numeric read-out and comparable graphic display. Here, we describe a simple method for the reliable and reproducible evaluation of signals generated on membranes or photographic films which combines standard graphics software with a low-budget desk top scanner.