As a basic operation of mechanical process engineering, pressure filtration and its scale-up has been described in detail in the literature. But, the pharmaceutical development of active substances, in particular, calls for a scale-up of relatively small quantities to execute downstream processes in a lean and reliable manner. Therefore, development depends on conclusions from smaller filter equipment. In this study, results from laboratory nutsche filters with filter surface areas of 1.4 cm(2) and 9.6 cm(2) were compared with results from a 20 cm(2) nutsche. It has been shown that no reproducible and reliable data could be generated using the 1.4-cm(2) nutsche. While this was possible using the 9.6 cm 2 nutsche, the permeability was greater than with the recommended 20 cm(2) nutsche so that a correction factor has to be introduced.