A simple one-step purification method, using expanded bed, ion-exchange chromatography, for the fractionation of nisin Z produced by Lactococcus lactis subsp. lactis A164 was developed. The highest dynamic binding capacity (0.92) of the adsorbent was obtained at a superficial velocity of 367 cm h(-1), resulting in approx. 2.7-fold bed expansion. The range of pH for the maximum adsorption was 3-4. The isocratic elution with 0.15 M NaCl led to approx. >90% recovery. Single-step purification of nisin Z from unclarified A164 culture broth resulted in 31-fold purification with a 90% yield.