The extracellular polymer substances (EPS) of Pseudomonas aeruginosa, alginate isolated from this EPS and an algal alginate were examined with analytical ultracentrifugation. The samples were dissolved in isotonic sodium chloride solution to avoid disturbance of the measurements due to polyelectrolyte effects. The sedimentation and diffusion coefficients were determined from velocity runs. Evaluation of sedimentation-diffusion equilibrium at medium centrifugal fields yielded molar masses and the second osmotic virial coefficients. The aim of this thesis was to determine differences in the thermodynamic properties of the polymers, the effect of acetylic groups on the aggregation of alginates and the influence of alginate on the stability of EPS. Additionally the gelation of alginates with calcium ions was examined both with an analytical ultracentrifuge and a dynamic oscillating rheometer.