Among the established plant cell lines, tobacco BY-2 cell line is unique, as it can be highly synchronized by established procedures. Because of this reason, the cell line has become invaluable for various studies, particularly on cell cycle issues. The importance of several characteristics of the cell line, some of which have not been handled thus far, is described in this article. We also include some preliminary characterization of an auxin-autotrophic cell line 2B-13 derived from the BY-2 cell line. Thus, the repertoire using the BY-2 cell line in plant sciences is expanding. The importance of this cell line could increase further as the expressed sequence tag (EST) database of the cell line became publicly available recently. The scientific achievements on this cell line that have been accumulated in recent years are being compiled and will be published as the 53rd volume in the monograph series of Biotechnology in Agriculture and Forestry (Nagata et al., 2004); readers are referred to this source.