A procedure is described for the isolation of a DNA photoreactivating enzyme from Streptomyces griseus. Application of chromatography on spherosil, ultraviolet-irradiated DNA-cellulose, DEAE-cellulose and single stranded-DNA-agarose resulted in a 22 000-fold purification with 46 percent recovery on the initial activity. According to polyacrylamide gel electrophoresis the final preparation was virtually homogeneous. The absorption spectrum of the enzyme exhibited a marked absorption band in the 400-460 nm region in addition to protein absorption.