The study was undertaken to establish the conditions of culture <em>in vitro</em> of <em>Chara vulgaris</em> L. antheridium isolated from the mother plant and to ascertain the regularities in the development of the antheridial filaments under these conditions. The culture of isolated antheridia was run for 5 days on Forsberg medium. The antheridial filaments were found to preserve their full viability evaluated in terms of ³H-phenylalanine incorporation With simultaneous depression of mitotic activity. Under these conditions a considerable part of the filaments pass through at least three division cycles. <em>In vitro</em> culture of isolated antheridia causes the greater shortening of the cell length the longer the antheridia are kept Isolated from the thallus.