Digoxin, digitoxin and acetyldigitoxin are the most widely prescribed of cardiotonic glycosides. Analytical exploration can be performed by a single assay when only one compound is prescribed or by multiple assays in cases of imprecise prescription or when several glycosides are given concomitantly. In addition, the metabolic transformation of digitoxin into digoxin and the presence of endogenous \"digitalis-like compounds\" mean that a number of precautions must be taken during prescription. These examples underline the ambiguity of the so-called \"digitalinaemia\" prescriptions and the need for biologists to be supplied with maximum information by clinicians.