A general fluorimetric method was developed for determination of noradrenaline, adrenaline, dopamine and serotonin in a single sample. Purification of samples was carried out on columns of Dowex 50X4 and 10 in sodium form. As judget by an internal standard the yield of noradrenaline and adrenaline was about 90% and of dopamin -- about 75%. Serotonin was determined by means of a condensation reaction with ninhydrin. A more stable fluorescence of serotonin samples was provided by an increase in warming-up time up to 55 min. Treatment of control probes with iodine solution permitted to eliminate an unspecific fluoresence of the tissues studied. The yield of serotonin was about 75% as estimated by an internal standard.