A 32-kb region including the Adh structural gene was analyzed with six restriction endonucleases in 20 lines of Drosophila pseudoobscura, one line of D. persimilis, and one line of D. miranda. Nineteen lines of D. pseudoobscura from a single population were estimated to be polymorphic at one in every 15 nucleotides (p = 0.066). Any two homologous chromosomes chosen at random were heterozygous at one in 48 (H = 0.021) nucleotides. Two small insertions of 50 and 200 bp were found approximately 7 kb upstream from the Adh transcript. High haplotype diversity and low linkage disequilibrium suggest that the polymorphic restriction sites around Adh have segregated almost randomly during the history of this D. pseudoobscura population and that the effects of inbreeding and periodic reduction of population size have been negligible. The restriction-endonuclease analysis for the Adh region of D. pseudoobscura stands in sharp contrast to the strong linkage disequilibrium, high levels of insertion/deletion polymorphism, and lower estimates of nucleotide polymorphism found for this same region in D. melanogaster. A phylogeny for the Adh haplotypes is consistent with an early divergence of D. miranda, while D. persimilis falls within the cluster of D. pseudoobscura haplotypes.