Abstract: A procedure to measure apoptosis in physiology and pathology in order to support clinical diagnosis and monitor efficacies of drugs and therapies. In particular a method for detecting and/or optionally quantifying and/or optionally isolating apoptotic cells in a sample, comprisingcontacting the sample with a detectable reagent having high affinity for phosphatidyl serine; andqualitatively and/or optionally quantitatively detecting cells that have reacted with the detectable reagent having high affinity for phosphatidyl serine preferably intact cells, detection occurring before or after an optional stepfor isolating apoptotic cells from non-apoptotic cells, which isolation can occur due to the fact that apoptotic cells have been provided with a detectable reagent having high affinity for phosphatidyl serine, the reagent also being selectable in a manner known per se. A suitable reagent having high affinity for phosphatidyl serine is a polypeptide or protein classified as an annexin.