Hollow chitosan fibers were tested for the diffusion of a series of biological macromolecules, including amino acids, vitamins, and antibiotics. The hollow fibers were immersed in the permeant solution, and water was circulated and recycled inside the lumen of the fiber. The concentration of the permeant in the hollow fiber loop was analyzed online by ultraviolet-visible spectrophotometry. The effect of process parameters such as the concentration, pH, and flow rate was tested. The permeability coefficient was calculated from the permeability. The limited influence of the flow rate indicated that resistance to film diffusion (at the surface of the fiber) was not the rate-limiting step: the limiting step remained diffusion through the membrane. The pH would be expected to influence the protonation of chitosan amine groups and the acid-base properties of the permeant; however, the diffusion profiles were little affected by this parameter. The impact of pH on the permeability coefficient decreased in the following order: tryptophan > chloramphenicol > vitamin B12. The change in the concentration of the permeant had a limited impact on the permeability coefficient. (c) 2007 Wiley Periodicals, Inc.