Objective: In a human leukemic megakaryocytic cell line HIMeg, differentially expressed genes regulated by induced differentiation will be cloned, and from which the key genes in the process of induced differentiation will be identified. Methods: The human megakaryocytic leukemia cell line HIMeg was treated with 13-cis retinoic acid for 4 d, then total cellular RNA was extracted and reverse-transcribed to first strand cDNA. The first strand cDNA was subjected to PCR-based mRNA differential display, cloning and sequence analysis. Results: From 5 cDNA fragment candidates obtained, RNA dot blot analysis demonstrated non-regulation in 3 fragments, undetectable signals in one fragment, and altered gene expression in one cDNA fragment which was designated MDI-1 (mRNA downregulated after induced differentiation).The nucleotide sequence data reported here will appear in the GenBank under the accession number AF026526. Conclusion: A cDNA fragment encoded by a unknown gene was cloned. Further studies are required to determine its full length sequence, gene structure and biological function(s).