The objective of the study was to verify the possibility of using membrane filtration techniques for partial separation of biologically active proteins from an egg white. Such proteins show a biological activity of both the lysozome, i.e. a muramidase enzyme of a molecular weight being 143·10² Da, and the cysteine proteinase inhibitor, i.e. a cystatin having a molecular weight of 126·10² Da. The microfiltration process of a native egg white and its solutions, prepared using a 0.15 M NaCl (the ratios were 1:1 and 1:4) was performed using a crossflow technique; tubular filters of polypropylene were used, their porosity being 0.2–0.6 µm. In the filtrates produced, the activity of lysozome and cystatin was determined (regarded as the ability to inhibit cystein proteinase – papaine), and it was stated that amounts of active, low weight substances recovered ranged from 60% to 80%. The fouling phenomenon had a key effect on the entire process efficiency; it was the creation of a new protein layer on the membrane. The new layer on the membranegenerated a decrease in the filtration rate. On the other hand, owing to the said new layer on the membrane, there was an improvement in enriching permeates with low weight active substances. As soon as more than 20–30% of the egg white processed have been filtrated, an essential increase in the activity of cystatin was stated compared to the initial solution.