Dehydrins are proteins produced during the late stages of plant embryo development and following any environmental stimulus involving dehydration. In order to investigate the variability of a dehydrin-encoding gene (Dhn1) in cultivated and wild sunflower (Helianthus annuus) genotypes, near-complete alleles were isolated by the polymerase chain reaction and sequenced. All of the isolated sequences were found to contain the typical dehydrin domains, and interrupted by an intron. The number of nucleotide substitutions and indels per site was calculated. With respect to the overall sequence, variation in both the coding and noncoding [intron and 3'-UTR (untranslated region)] sequences was much larger among wild accessions than among cultivars. No variation was observed in 3'-UTRs from cultivated sunflowers. Different coding regions showed a different numbers of synonymous and nonsynonymous substitutions. The Y and K domains were the most conserved in both wild and cultivated genotypes. Sequence analysis of the deduced dehydrin proteins showed that nucleotide substitutions in wild accessions should also determine large biochemical differences at the protein level. All of the isolated alleles were however functional, at least at the transcription level. To our knowledge these are the first data on intraspecific genetic variability of such a stress response gene. The low variability of dehydrin genes from cultivated sunflower is discussed in relation to the origin of sunflower cultivars. The possibility of rescuing general genetic variability through crosses to wild accessions of H. annuus rather than using wild Helianthus species is also discussed.