At the Institute of Occupational Medicine and Environmental Health, during 12 years, chronic mercury intoxication was diagnosed in 34 persons. There were male workers tending technological processes in which Hg was used as a catalyst (synthesis of acetic aldehyde and obtaining chlorine). The length of professional exposure was 13-34 years (mean 20.6). The patients were removed from the contact with Hg after Hg intoxication case was confirmed. During the following 11 years, 24 of them were reexamined in the clinical department 2-4 times. The clinical picture of the poisoning consisted mainly of neurasthenic, cerebellar (30 persons), psychoorganic symptoms (20 persons) and behavioural changes (irritability, aggressive states). Headaches, sleep and recent memory disturbances, progressive behavioral changes, dizziness, were the most frequent complaints. The authors stressed the irreversibility of central nervous disorders despite cessession of the exposure to Hg. The degree of cerebellar intensity changes did not handicap examined patients. This is especially important to show the difference between the above described clinical picture of Hg intoxication and multiple sclerosis.