EURONEST, a concerted action of the European Community with the participation of most EC and some COST countries, is a project aimed at studying the epidemiological impact of CNS effects from protracted exposure to industrial chemicals in the participating countries. After a review of current knowledge, the paper examines the structure and detailed aims, i.e., the qualitative and quantitative study of exposure to neurotoxic chemicals, the performance of an investigation to contribute to the controversial issue of organic solvents CNS toxicity, the definition of the solvent-induced psychoorganic syndrome as well as its epidemiological relevance, and the influence of exposure on the quality of life, in particular on aging. The primary target population consists of workers with long-term exposure to toluene in the printing industry to establish CNS effects and no-effect level; depending on local priorities mixed solvents exposure can also be investigated. The study design is an ambidirectional cohort and sample size requirements are given. The approach as to the methods is not to choose at once among the available neurobehavioral batteries, but to produce a register of the 20-25 tests more commonly used in the different participating laboratories, in order to examine their validity, sensitivity, and reliability. From this exercise, a new more flexible battery is expected to be more effectively applicable under different conditions. Criteria for clinical diagnosis of the solvent-induced psychoorganic syndrome are given in order to be utilized in the investigation of the prevalence rates of these disorders included in the concerted action's program.