Drebrins are developmentally regulated proteins found in chicken brain and are classified into two forms of the embryonic type (E1 and E2) and one form of the adult type (A). Although the time courses of their appearance are different from each other, the structures of the 3 forms are closely related. Two kinds of drebrin cDNA, designated gDcw6 and gDcw17, were isolated from the cDNA library of the chicken embryo and their nucleotide sequences were determined. Their sequences were entirely identical except for a deletion of an internal 129-nucleotide sequence, and the gDcw17 insert contained an open reading frame capable of encoding 607 amino acids. These cDNAs seemed to correspond to two embryonic forms of drebrin mRNAs. The predicted drebrin molecules are highly hydrophilic and have proline-rich sequences and long stretches of glutamate in the carboxyl-terminal region. RNA dot-blot analysis using the drebrin cDNA as a probe demonstrated that the amounts of drebrin mRNAs were also developmentally regulated as those of drebrins. Southern blot analysis showed that the chicken genome has a single copy of the drebrin gene per haploid complement. These findings suggest that the multiple forms of drebrins result from alternative splicing of the single drebrin gene during neural development.