Single-strand-conformation polymorphism (SSCP) of ribosomal DNA of 29 species (282 isolates) of Phytophthora was characterized in this study. Phytophthora boehmeriae, Phytophthora botryosa, Phytophthora cactorum, Phytophthora cambivora, Phytophthora capsici, Phytophthora cinnamomi, Phytophthora colocasiae, Phytophthora fragariae, Phytophthora heveae, Phytophthora hibernalis, Phytophthora ilicis, Phytophthora infestans, Phytophthora katsurae, Phytophthora lateralis, Phytophthora meadii, Phytophthora medicaginis, Phytophthora megakarya, Phytophthora nicotianae, Phytophthora palmivora, Phytophthora phaseoli, Phytophthora pseudotsugae, Phytophthora sojae, Phytophthora syringae, and Phytophthora tropicalis each showed a unique SSCP pattern. Phytophthora citricola, Phytophthora citrophthora, Phytophthora cryptogea, Phytophthora drechsleri, and Phytophthora megasperma each had more than one distinct pattern. A single-stranded DNA ladder also was developed, which facilitates comparison of SSCP patterns within and between gels. With a single DNA fingerprint, 277 isolates of Phytophthora recovered from irrigation water and plant tissues in Virginia were all correctly identified into eight species at substantially reduced time, labor, and cost. The SSCP analysis presented in this work will aid in studies on taxonomy, genetics, and ecology of the genus Phytophthora.