The polyene antibiotic candicidin produces a rapid efflux of K(+) ions from a suspension of Candida albicans. Onset of K(+) leakage depends on the culture age, stationary-phase yeasts leaking K(+) more slowly than exponential-phase yeasts. The time taken for potassium leakage to begin represents the time taken by the antibiotic to cross the cell wall and produce membrane damage. It was shown that there were factors in the cell wall of C. albicans that increased their total binding capacity and their affinity for candicidin during growth. An attempt was made to relate changes in the lipid content of the yeast cell with the increased time taken to produce membrane damage.