DNA polymorphisms among Magnaporthe grisea isolates from rice and from finger millet were examined using restriction analysis of genomic DNA. The rice-infecting isolates produced 50–70 resolvable EcoRI fragments with the rice blast-derived repetitive sequence probe MGR586, while isolates infecting finger millet showed only one prominent band. Probes derived from a repetitive sequence (grasshopper) from a finger millet also distinguished the two pathogenic forms; grh pES 3–3 (35–70 EcoRI RFLPs) and grh pKE 2–2 (2–12 EcoRI RFLPs) hybridized exclusively with isolates infecting finger millet. Probes of two avirulence genes derived from rice blast genomes hybridised exclusively with rice blasts. These distinctions in Indian blast populations matched those observed elsewhere in Asia and in the Americas. No genomes were observed in the field that shared RFLPs from rice-infecting and finger millet-infecting isolates, even among isolates from a Himalayan area where the two forms have coexisted for centuries. Pathogenicity tests showed that the blast fungus from the two hosts did not cross-infect, nor did the two forms cross in the laboratory. The results confirm that the rice and millet-infecting M. grisea populations in India are distinct.