A method for detecting the presence of a lysed eukaryotic cell in a sample, said method comprising: (i) adding adenosine diphosphate (ADP) to said sample under conditions which allows the conversion of ADP to adenosine triphosphate (ATP) by cellular adenylate kinase, (ii) detecting ATP in said sample and relating that to the presence of adenylate kinase and thus to the presence of lysed cells. The method is useful in detecting the cell lysis, for example when screening for drugs which are required to cause lysis, for example for use in tumor therapy. However, in addition, cells may, in a preliminary step, be lysed and the contents quantitated in order to establish for example the health of condition of the cells or to detect the presence of cells in sample such as milk or urine, for diagnostic purposes.