A method of detecting a molecule associated with viability of one or more cells or organisms in a sample comprises the initial step of contacting the sample with an enzyme, which enzyme is capable of adding or removing a chemical moiety to or from a nucleic acid molecule in the presence of the molecule associated with viability of the of the one or more cells or organisms. This thereby generates a novel detectable nucleic acid molecule. The next step involves detecting the presence of the molecule associated with viability of the one or more cells or organisms by detecting the novel nucleic acid molecule generated only in the presence of the molecule associated with viability of the one or more cells or organisms. A most preferred molecule associated with viability is ATP, although NAD may also be detected. A preferred enzyme for use in the methods is ligase. The method has numerous applications, in particular in monitoring viability of cells, toxicology testing and determining whether there is contamination in a sample or on a surface. Kits are also provided for carrying out the methods.