Polygalacturonase inhibitors have been reported in a number of dicotyledonous plant tissues including pear and raspberry fruits and bean seedlings. These proteins inhibit fungal polygalacturonases and thus have been implicated in disease resistance in plants. The earlier work on the inhibitor from bean plants was conducted with hypocotyls as the source. We have found that immature bean pods contain much more inhibitor than other parts of the plant and developed a procedure for purification of this inhibitor. Fresh bean pods were extracted with 1.0 M NaCl at pH 7 and the proteins were precipitated with ammonium sulfate. The proteins were dissolved, dialyzed and chromatographed on a column of S-Sepharose. The inhibitor from this step was then chromatographed on a Mono Q column at high pH. Yields of the inhibitor varied somewhat with bean cultivar and pod maturity but were about ten times higher than from hypocotyls. The purified inhibitor reacted optimally with Aspergillus niger endopolygalacturonase at pH 4.3 and appeared to be similar to the inhibitor from hypocotyls. Bean pods thus are a convenient source of polygalacturonase inhibitor for studies on fruit maturation and disease resistance in plants.