The ATP-binding cassette (ABC) superfamily of membrane transporters has been implicated to play a role in pathogenesis in various phytopathogenic fungi. In an insertional mutagenesis screen for pathogenicity mutants of Magnaporthe grisea obtained via Agrobacterium tumefaciens-mediated transformation (ATMT), a novel gene belonging to the ABC transporter family was identified. The gene ABC4 was predicted to be 5045 bp in length coding for a protein of 1654 amino acids. The mutant did not form functional appressoria and was nonpathogenic. When compared with wild type, the mutant showed increased sensitivity to certain antifungal compounds and phytoalexins, implying the role of ABC4 in multidrug resistance (MDR) as well as establishment in the host. Reverse transcriptase PCR showed the expression of ABC4 in wild-type strain while it was absent in the mutant abc4. In real-time PCR, the expression of ABC4 was seen to be enhanced in the presence of various drugs tested. The data suggests that ABC4 is required for the pathogenicity of M. grisea, helping the fungus to cope with the cytotoxic environment during infection.