Flow cytometric analysis of nuclear DNA contents of somatic tissues of cabbage (Brassica oleracea L.) has revealed extensive endopolyploidization, resulting in tissues that comprise mixtures of cells with different DNA contents, ranging from 2C to 16C. Patterns of endopolyploidy are specific to each developmental stage. Multiple polyploidy was not present in the embryos of dry seeds. Rapid endoreduplication occurred in the radicle and the hypocotyl of the embryos during seed germination. Further endoreduplication cycles were detected in all tissues except those of the shoot tips. In five cabbage cultivars tested, seedlings contained cells of four ploidy levels, corresponding to 2C; 4C, 8C and 16C. Multiploidy may be an integral part of differentiation programs in cabbage plants. The biological significance of endoreduplication in cabbage plants is discussed. (C) 2001 Annals of Botany Company.