In the clinical development of [124I]SIB–annexin V for cancer therapy monitoring, additional measures of viability, for example, the exchanging H215O space in tissues by PET (Wilson et al, 1992) or T2 relaxation maps by MRI (Heywang et al, 1987), may be required to differentiate between apoptosis and necrosis. The gene discussed is ANXA5; the disease is cancer.