The cotton (Gossypium hirsutum L.) germplasm, Auburn 634 and others derived from this source, contain resistance genes that effectively inhibit reproduction of root knot nematode (Meloidogyne incognita [Kofoid and White] Chitwood, race 3). Although infective root knot nematode juveniles penetrate the resistant cotton lines in numbers similar to susceptible lines, nematode development is arrested in the resistant lines soon after infection. Analyses of root proteins via one- and two-dimensional polyacrylamide gel electrophoresis (PAGE) revealed a relatively abundant 14 kilodalton (kDa) polypeptide that was differentially expressed in resistant isoline 81-249 at 8 d after inoculation. Dissection of nematodes from equivalent root samples and their analysis separate from the root tissue showed that the 14 kDa was a plant protein. Expression of the 14 kDa protein in infected roots of 81-249 was localized to the nematode-induced galls. Digestion of the polypeptide with cyanogen bromide (CNBr) yielded two major fragments of 9 and 4 kDa from which partial amino acid sequences were obtained. Comparison of these partial sequences with gene databases did not reveal strong homologies with other sequences. Thus, the 14 kDa protein may represent the product of a novel, root knot nematode-inducible plant gene whose expression is temporally correlated with the resistance response to root knot nematode.