Previous findings by our group have shown how primordial male germ cells take part in regenerative blastema formation in planarians by migrating to the wound. The role of these cells in rebuilding transected tissues has been investigated in a population of Dugesia lugubris s.l. which is particularly suited for our purpose. In fact, these planarians provide a clear karyological marker to distinguish diploid male germ cells (2n = 8) from tryploid embryonic or somatic cells (3n = 12). In this study we employed the cytophotometric analysis of the nuclear Feulgen-DNA content in order to distinguish non-replicating male germ cells from reserve and somatic cells. The Feulgen-DNA content in cells from the gonad-free caudal area was measured after complete regeneration. Most non-replicating cells (94-95%) were found to have a DNA amount typical of cells previously estimated as triploid. Some (5-6%) nuclei containing a DNA amount typical of cells previously estimated as diploid male gonia were also found. These findings seem to support the view that primordial male germ cells also participate in rebuilding somatic tissues according to the field influence they encounter during regeneration. The possibility that metaplasia (or cell transdifferentiation) may occur in planarians is finally discussed.