The problem of the origin and nature of blastema cells in planarians has been karyologically investigated in a population of Dugesia lugubris s.l. in which the somatic line is triploid (12 chromosomes), the female germ line is hexaploid (24 chromosomes) and the male germ line is diploid (8 chromosomes). Sexually mature specimens were transected at a cephalic level anterior to the ovaries: from each transected specimen two regenerants were obtained both of which formed a blastema. Forty-two hours after the transection most of the metaphasic cells of the posterior regenerant blastemata (p.r.b.) had 12 chromo somes. In some p.r.b. hexaploid cells, interphasic double-nucleated cells and cells with 8 chromosomes were also found. By contrast, in the blastemata of anterior regenerants (lacking gonads) only triploid cells were found. The possible contribution of germ cells to the blastema formation in planarians is discussed.