Abstract : The luminol reaction may serve very well for the detection of blood spots and traces of blood on various objects in judicial-medical and criminological practice. There are various recipes for preparing the luminol reagent, among which that with sodium hydroxide yields equally intensive chemiluminescence regardless of whether it is a matter of fresh traces of blood (oxyhemoglobin) or dried spots (methemoglobin). The reagents with sodium carbonate or with sodium perborate, on the contrary, yield stronger luminescence with dried blood spots than with solutions of fresh blood under otherwise like experimental conditions. The clarity of this reaction is exceptionally great. The correct manner of effecting this reaction to detect blood spots is shown, and the results of the quantitative measurements concerning the influence of various natural substances on the chemiluminescence of luminol are given. Both catalytic and inhibitory effects were noted in the action of these substances.