Maltoporin has been purified by affinity chromatography on starch gel columns. This single-step procedure affords the rapid purification of active protein from wild-type and mutants of E. coli, and from other Gram-negative bacteria. The monodisperse protein was crystallized under various conditions. Several preparations have yielded crystals amendable to X-ray analysis, notably a single cysteine substitution, S57C. (C) 1994 Academic Press, Inc. Maltoporin