We have identified five fiber-specific cDNA clones from cotton (Gossypium hirsutum L.). Three of these clones were further characterized in terms of their transcript sizes, protein products, gene numbers and conservation in other plant genomes. Clone E6 codes for two abundant transcripts of 0.9 and 1.0 kilobases (kb) and proteins of 26 and 30 kilodaltons (kDa). Clone B8 hybridizes to an RNA of 1.1 kb and codes for a protein of 22 kDa. Clone H6 hybridizes to an RNA of 0.9 kb. Southern blot analysis of cotton genomic DNA shows that E6, H6 and B8 are encoded by one or two genes each. Homologous sequences to E6, B8 and H6 were not detected in tobacco, soybean, and maize DNA. All three genes are developmentally regulated. Profiles of relative steadystate concentration of RNAs homologous to these clones follow a biphasic course during development. The above characteristics of these genes are suggestive of functions in cellulose synthesis and/or deposition in cotton fiber. However, confirmation of their functions must await development of in-vitro cell-free cellulose synthesizing systems and characterization of fiber mutants.