Vergleichende Untersuchungen zur biologischen Aktivität von Chitosanen in Relation zu ihren physikalisch chemischen Eigenschaften Chitosans are a diverse group of biopolymers which are widely used in different fields of application for years. They are appreciated and used especially because of their antimicrobial effects combined with their biocompatible properties. However details of the correlation between their physical chemical characteristics and biological effects (e.g. antimicrobial effect) have not been fully understood yet. In the following thesis the antimicrobial properties were examined with mold fungi as well as with gram positive and gram negative bacteria. Furthermore the biocompatibility was proven with a plant assay and the physical chemical properties of chitosan were systematically investigated. The results of the investigations on mold fungi and bacteria allow the conclusion that chitosan has no antifungal capacities. Furthermore the mold fungi are able to use the chitosan as carbon resource. Certainly chitosans operated as an inhibitor to the group of bacteria. They acted biostatical and bactericide which led to a structural membrane damage of E. coli. However there was no indication of a different effect on gram positive bacteria compared to gram negative bacteria. The effect of chitosans is presumably more affected by bacteria and their adaptation to the environment rather than by the composition of the membrane structure. It was shown that the marine gram negative bacteria V. fischeri was less affected in the occurrence of luminescent than the bacteria E. coli (gram negative) and B. subtilis (gram positive) in their dehydrogenase activity. The biocompatibility is guaranteed unrestricted as long as the pH is neutral to alkaline. Chitosans will form micelles or aggregates under these pH conditions which significantly reduces their bioavailability. Effects in eukaryotic test systems under acetic pH conditions demonstrated that the chitosan significantly disturbed the growth of the plant L. minor. Additionally no growth recovery was observed even several weeks after the treatment. No influence of the molecular weight of the Chitosans on inhibition effects could be found for the correlation of the physical chemical properties with all EC values over all experiments. On the other hand it could be shown that the degree of acetylation (and additionally combined with the amount of acetylated units) and the pattern of acetylation might influence the impact of chitosan on biological effects. A low degree of acetylation or a low numbered pattern of acetylation inhibited the growth of bacteria most clearly whereas a high degree of acetylation or a high numbered pattern of acetylation inhibited the growth of L. minor most effectively. Complete biocompatibility can probably be achieved by adaption of these characteristics of chitosan.