The effects of low molecular weight (96.5 KDa) chitosan on the pathogenic yeast Candida albicans were studied. Low concentrations of chitosan, around 2.5 to 10 μ g·mL(-1) produced (a) an efflux of K(+) and stimulation of extracellular acidification, (b) an inhibition of Rb(+) uptake, (c) an increased transmembrane potential difference of the cells, and (d) an increased uptake of Ca(2+). It is proposed that these effects are due to a decrease of the negative surface charge of the cells resulting from a strong binding of the polymer to the cells. At higher concentrations, besides the efflux of K(+), it produced (a) a large efflux of phosphates and material absorbing at 260 nm, (b) a decreased uptake of Ca(2+), (c) an inhibition of fermentation and respiration, and (d) the inhibition of growth. The effects depend on the medium used and the amount of cells, but in YPD high concentrations close to 1 mg·mL(-1) are required to produce the disruption of the cell membrane, the efflux of protein, and the growth inhibition. Besides the findings at low chitosan concentrations, this work provides an insight of the conditions required for chitosan to act as a fungistatic or antifungal and proposes a method for the permeabilization of yeast cells.