A technique was standardised to develop callus cultures from leaf tissues of tobacco plants infected with CPO strain of tobacco mosaic virus. These leaf callus cultures had a higher virus titre than the callus cultures developed from other explants such as stem, as evidenced by bioassay on local lesion hosts. Morphogenetic dedifferentiation of callus culture influenced the virus titre of the cultured tissues. Caulogenic dedifferentiation of the callus culture induced higher virus titre than rhizogenic dedifferentiation. In the non-differentiated callus cultures, however, the introduction of histogenesis, as evidenced by the compact growth, did not affect the virus titre. The formation of chlorophyll in the callus culture cells also did not change the infectivity of the tissue and thereby the virus titre.