The present review draws a general picture of the bioanalytical applications of electro-chemiluminescent reactions (ECL). Only the two main ECL reactions-i.e. the luminol-based and Ru(bpy)(3)(2+)-based reactions-are considered for application in the fields of enzyme biosensors, immunochemical biosensors, DNA biosensors, and biochips. The mechanism, principle, and experimental conditions of these two reactions are described. Then, for each category of analytical tools, experimental set-ups and performances are presented and discussed.