The new method of biological assessment in flowing waters-NoMBSI (Non-lethal Method for Benthos Sampling and Identification) is presented. To determine the amount of information (informativity), which is possible to obtain during a sample analysis, the results of three procedures were compared (NMthe new one based on 3D digital image analysis, NCcontrol procedure based on microscopic identification and G, which is the traditional method based on samples collected with Günther sampler). Procedures were applied for the samples collected at 27 sites in North-eastern and Eastern Poland. The NM was found to provide for the correct recognition of an average of 45% of taxa present in samples. Taxa of small size and lower abundance were frequently failed to be identified. However, no significant differences between NM and NC in terms of raw data on taxonomic composition were found, while the results of G procedure were significantly different when compared with both other procedures. Values of commonly used biotic and diversity indices calculated on the basis of those procedures were compared using correlation. The level of identification achieved sufficed for the proper determination of water quality classes at all of the sites sampled.