Deoxyribonucleic acid was extracted from the late blight fungus, Phytophthora infestans, and partially characterized in terms of its physical and chemical properties. Hydrolysis of the purified DNA followed by electrophoretic analysis failed to demonstrate the presence of constituents other than those characteristically found in DNA. Analysis of the nucleotide composition based on thermal denaturation studies yielded values for the percentage guanine–cytosine which are consistent with those reported for other members of the Phycomycetes.