We have expressed two antifreeze protein genes from the Atlantic wolffish, Anarhichas lupus, in Drosophila melanogaster by placing them under the divergent transcriptional control of the host yolk polypeptide (1 and 2) gene promoters. Both genes were joined to the central promoter region by fusion within the DNA encoding the signal polypeptides. The chimeric genes were introduced into flightless mutant Drosophila through P-element transformation. Transformed adult females from individual lines accumulated 1.5-5 mg/ml of antifreeze protein in their hemolymph. The protein was purified to homogeneity from hemolymph following thermal denaturation, step elution from SP-Sephadex, and reverse-phase HPLC. It was recovered in high yield and retained full biological activity even though one of the two gene fusions gave rise to a seven amino acid N-terminal extension on its antifreeze protein product.