A Drosophila melanogaster gene encoding a homologue of the mammalian ER calcium binding protein, calreticulin, was cloned and the nucleotide sequence determined. Four exons can be identified, contained within 1700 bp of sequence, separated by introns of 124, 266 and 92 bases. The exons encode a 389 amino acid protein which may be a precursor form as it includes an N-terminal signal region of 17 residues that could potentially be cleaved to form a mature protein. The C-terminal region of the protein contains the established pattern of polyacidic clusters, common to calreticulins of other species and ends in the ER retention signal HDEL. Excluding the N-terminal signal region, the Drosophila protein amino acid sequence has a 67% identity to mammalian calreticulins and the length and acidity of the C-terminal zone in the insect protein are intermediate between higher mammalian and lower nematode values.