A cloned Drosophila heat shock protein 22 gene was transfected into two independently established Drosophila cell lines. Each line carried a different heat shock protein 22 allele, distinguishable by electrophoresis of the protein. The transfected gene was not expressed at 25 degrees C but could be induced at 36 degrees C. In one line, two heat shock protein 22 electromorphs were synthesized.