Ceruloplasmin (CP) is a plasma glycoprotein that transports copper throughout the body. In previous studies (Yang, F., Naylor, S., Lum, J., Cutshaw, S., McCombs, J., Naberhaus, K., McGill, J., Adrian, G., Moore, C., Barnett, D., and Bowman, B. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 3277-3261), two CP cDNA clones, CP-1 and CP-2, from a human cDNA library, differed from each other by the presence or absence, respectively, of 12 nucleotide bases encoding a deduced sequence of Gly-Glu-Tyr-Pro near the carboxyl-terminal region of the ceruloplasmin molecule. Examination of genomic DNA demonstrates that the two CP mRNAs are produced from a single gene by alternative spliced patterns. The additional amino acids deduced in CP-1 are products of alternative splicing within an intron of the CP gene at a site 12 nucleotide bases 3' to the commonly used site of CP-2. The CP-1 mRNA transcript encoding four extra amino acids appeared as a minor species accompanying CP-2 mRNA in placenta and chondrocytes. CP-1 mRNA was the predominant CP transcript in a lymphoblastic leukemia cell line, CEM. The mRNA examined from other tissues contained only CP-2 mRNA transcripts. These findings predict that alternative RNA splicing may lead to the differential expression of CP genomic sequences and produce alternate isoforms from a single CP gene in specific tissues.