A recently identified gene encoding a metalloprotease-like, disintegrin-like, cysteine-rich protein (MDC) represents a candidate tumor suppressor gene for human breast cancer based on its location within a minimal region of chromosome 17q21 previously defined by tumor deletion mapping. The work reported here has shown that the MDC gene consists of 28 exons interrupted by relatively short introns, most of them 67 bp to 5 kb in length. We have identified two forms of transcripts generated by alternative splicing. The more abundant form encodes a protein of 769 amino acids; the other, a previously described cDNA, encodes 524 amino acids. Exons 1a, 1b, 1c, 1d, and 2–7 encode a proprotein domain; exons 7–13, a metalloprotease-like domain; exons 14–17, a disintegrin domain; exons 18–22, a cysteine-rich domain, including an epidermal growth factor (EGF)-like repeat domain within exons 21 and 22; exon 23, a transmembrane domain; and exons 24 and 25, a short cytoplasmic domain. These results show that human MDC contains a mosaic of exons capable of encoding several functional