The expression of and á-tubulin proteins in developing fibers and several other tissues of cotton (Gossypium hirsutum, cv. Texas Marker 1) have been analyzed using one and two-dimensional gel electrophoresis and immunoblotting. As a percentage of total protein, fibers appeared to have greater amounts of tubulin than hypocotyls, roots, leaves or cotyledons. Both and á tubulin, having molecular masses of approximately 50 kD and isoelectric points between pH 5 and pH 6 were resolved on a single two-dimensional gel. Under the conditions used -tubulin appeared to be less acidic in the IEF dimension and migrated slightly faster in the SDS dimension than á-tubulin. Nine -tubulin isotypes which formed two distinct groups were identified on immunoblots of two-dimensional gels. The three most abundant -tubulin isotypes were common to all tissues examined. Seven distinct á-tubulin isotypes were also identified. Although their level of accumulation differed, four of the á-tubulin isotypes were common to all tissues. Preferential accumulation of isotypes was most apparent in fibers than in the other tissues examined. Two -tubulin isotypes and two á-tubulin isotypes showed preferential accumulation in 10 and 20 days-post-anthesis fibers, respectively.