Regional cerebral blood flow was measured in patients with the diagnosis of chronic toxic encephalopathy induced by exposure to organic solvents. Measurements were made at the time of diagnosis and 24-84 months after the cessation of exposure. During the follow-up the patients were carefully examined for other possible causes of brain dysfunction. Comparisons were made to unexposed and solvent-exposed referents. At the first examination the patients had a 7% lower mean flow level than the unexposed referents and a 5% lower level than the exposed workers. The largest flow differences were seen in the frontotemporal areas. At the follow-up, the difference in the mean flow level between the patients and referents was no longer significant. Regionally, the flow had increased, especially in areas which initially showed the most pronounced decreases. There was a significant negative correlation between the initial cerebral blood flow level and the degree of normalization of the flow level at follow-up.