The chicken alpha A-crystallin gene and 2.6 kb of its 5' flanking sequence have been isolated and characterized by electron microscopy and sequencing. The structural gene is 4.5 kb long and contains two introns, each approx. 1 kb in length. The first intron divides codons 63 and 64, and the second intron divides codons 104 and 105, as in rodents. There is little indication that the insert exon of rodents (an alternatively spliced sequence) is present in complete form in the chicken alpha A-crystallin gene; small stretches of similarity to this sequence were found throughout the gene. The 5' flanking sequence of the chicken alpha A-crystallin gene shows considerable sequence similarity with other mammalian alpha B-crystallin genes. In addition, one consensus sequence (GCAGCATGCCCTCCTAG) present in the 5' flanking region of the chicken alpha A-crystallin gene was found in the 5' flanking region of most reported crystallin genes.