To date, increases in healthspan have not kept up with those in lifespan, and many elderly, despite surviving cancer and cardiovascular disease that would have once killed them, are in poor health overall. Recent studies have suggested that senescent cells, which are not dying but have stopped dividing, are contributors to the frailty that accompanies aging. Now a team from the Mayo Clinic has put that idea to the test directly, transplanting senescent cells into young mice.