The article deals with the optimization of conditions for the chemiluminescence determination. The Daphnia habitat was shown to have no spontaneous chemiluminescence. This was revealed using hydrogen peroxide and luminol, the optimal concentrations of which were 23 and 1.6 x 10(-2) mmol/L. p-Iodphenol at low concentrations (4 x 10(-5)-2 x 10(-3) mmol/L) did not render its effect chemiluminescence signal while at high concentrations (4 x 10(-2) mmol/L) an inhibition of chemiluminescence was observed. To obtain the needed intensity of chemiluminescence no more than 5 daphnia persons is required to incubate in volume of 10 mL of sample for analyzing. The intensity of chemiluminescence of daphnia cultivating medium and the sensitivity of this organism to potassium chromate increased at the temperature increasing from 24 to 32 degrees C. Daphnia cultivating medium can be preserved in refrigerator for several hours without lost of chemiluminescence signal.