[en] The aim of this paper is to summarize the observations of occupational exposed persons in the period from 1972 to 1992. The study covers different types of exposure - in uranium processing plants, NPP, medical and industrial facilities using ionizing radiation, and control groups of non-exposed persons. The results show an increased rate of neuro-vegetative dystonia in the groups submitted to chronic low dose irradiation, compared to the control groups. This is considered to reflect the non-specific adaptive reaction of the central nervous system to low intensity irritating factor. The neuro-vegetative asthenia is obtained only in subgroups of persons irradiated with doses above 45 mSv. This illustrates the quasi-threshold character of the organic radiobiological reactions dose-effect