Solution-phase chemiluminescent reactions of analytical interest are described. Their attractions include high sensitivity, wide dynamic range and the use of simple instrumentation for monitoring emission. Selectivity can be incorporated into such reactions by means of physical and/or chemical processes (either on-line or off-line). Practical considerations and the instrumentation required are also discussed. Specific applications of chemiluminescent reactions are classified according to the nature of the analyte, i.e.; inorganic species, enzymes and nucleotides, acids and amines, carbohydrates, steroids, polycyclic aromatic compounds and drugs, with the emphasis on recent applications and salient review articles.