AbstractIn platyhelminths, all cell renewal is accomplished by totipotent stem cells (neoblasts). Tissue maintenance is achieved in a balance between cell proliferation and apoptosis. It is known that in Macrostomum sp. the epidermis undergoes extensive cell renewal. Here we show that parenchymal cells also exhibit a high rate of cell turnover. We demonstrate cell renewal using continuous 5′bromo‐2‐deoxyuridine (BrdU) exposure. About one‐third of all cells are replaced after 14 days. The high level of replacement requires an equivalent removal of cells by apoptosis. Cell death is characterized using a combination of three methods: (1) terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labelling (TUNEL), (2) specific binding of phosphatidyl‐serine to fluorescent‐labelled annexin V and (3) identification of apoptotic stages by ultrastructure. The number of cells observed in apoptosis is insufficient to explain the homeostasis of tissues inMacrostomum. Apoptosis‐independent mechanisms may play an additional role in tissue dynamics.