The chicken ApoAI gene has been isolated and characterized. This gene contains three introns: the first is situated after nucleotide (nt) 41 in the 5'-untranslated region of the gene, the second interrupts the codon specifying the Gly-10 of the prepeptide, and the third disrupts the codon for Asp42 in the mature ApoAI protein. The chicken ApoAI gene has 62.6% sequence similarity with the human and 65.0% similarity with the rat gene. Intron-exon organization of the chicken gene is similar to that of human and rat ApoAI genes. Two different transcriptional start points (tsp), only 2 nt apart from each other, have been obtained for the chicken ApoAI gene. The 5'-flanking sequence of the gene contains TAAATA (TATA-like box) and CCACAT (CCAAT-like box) sequences, which are located 21 bp and 96 bp upstream from the tsp, respectively. This gene's sequence and structural organization provide a basis for future studies of the regulation of chicken ApoAI gene expression.