Midkine is a growth/differentiation factor which is found as a product of a retinoic acid-responsive gene. The 2.3-kb upstream sequence of the human MK gene has cis acting elements which confer retinoic acid-induced expression of fused chloramphenicol acetyl-transferase (CAT) gene in F9 embryonal carcinoma cells. In the 5'-region of the human gene, a sequence resembling the DR5-type retinoic acid-responsive element (AGGTCA-related direct repeats separated by 5 nucleotides) was present in a small block of highly homologous 5'-sequences shared by the human and mouse genes. Deletion of this direct repeat reduced retinoic acid-induced CAT gene expression. The core element in the human gene differs from the consensus sequence of retinoic acid-responsive element in two nucleotides and from the retinoic acid responsive element of the mouse MK gene in one nucleotide.