Currently available methods for diagnosis of chronic mercury intoxication (CMI) are applied at the any stage of the disease. Changes in these indices sometimes have no the specificity for any CMI stage, and a conclusion on them has the descriptive character. In addition, the above mentioned methods possess not sufficiently high accuracy in the diagnosis of intoxication at early stages of the development of the disease. The purpose of the research is the development of the method permitting to make the differential diagnosis between the initial symptoms of mercury poisoning and its first degree. 118 men who work/worked in the contact with mercury vapor were examined. There were evaluated electroencephalogram, long-latency auditory and cognitive evoked potentials, cerebral hemodynamics, noradrenaline (NA)content in the blood plasma. Statistical processing was performed with the use of «Statistica 6.0» software. The levels of NA in the development of CMI were shown to increase, by the time of the shaping of this disease the noted change was decompensated in the nature. The study of reactivity of cerebral vessels revealed the presence of abnormal responses during hypercapnic load in 14 - 24% of examined cases. In the analysis of auditory evoked potentials there was established the change in indices of latency and amplitude of the V- wave, which pronounced in the prolong response time, significant elongation in the P1 peak latency and the gain in the latency of N1 peak. There was established the presence of the wave-like change in the index of the latency of P300. In workers without an occupational disease, there was noted the marked elongation of the latent period of cognitive potential, while in patients with the newly made diagnosis the latency of P300 corresponded to standard values, and in the long term there was observed a sharp deterioration in this index. With the aid of the discriminant analysis with the calculation of canonical value there were revealed the most informative neurobiochemical indices, reoencephalogric ones and evoked potentials. The developed method of diagnosis allows to distinguish between the initial symptoms of mercury intoxication and the first stage of the disease.