A comparative study on the effects of acute exposure to mercury vapor in young adult monkeys. To establish the most appropriate species to use for the study of neurological and behavioral effects of mercury vapor (Hg vapor) in young adult monkeys, we studied changes in respiration, heart rate (HR), blood pressure (BP), and neurobehavioral functioning in 4 species: Macaca mulatta (monkey A), Macaca fuscata (monkey B), Macaca fascicularis (monkey C), and Cebus apella (monkey D). These results were compared with results in human beings exposed to Hg vapor in a previous study. Experiments were performed under the same general conditions (e.g., ambient temperature, light/dark cycle, and humidity), with the same method of Hg vapor inhalation, and using the same criteria for the criteria for toxicity, except that monkeys were exposed to lower concentrations (Hg vapor 20.0 micrograms/liter) than the present previous study. Mercury blood concentrations (total mercury) at which the symptoms appeared in monkeys were similar to those reported in human beings. These concentrations were lower than the Hg vapor exposure concentrations which produce adverse effects in monkeys. Therefore, the use of young adult monkeys is a suitable model for future studies. The respiratory, cardiovascular, and neurobehavioral effects of Hg vapor were more pronounced in monkey B and monkey C than in monkey A and monkey D. It may be concluded that the sensitivity of monkeys varies with species and the different behavioral systems. Monkeys A and B were most sensitive and monkeys C and D were the least sensitive. Further behavioral studies are needed to determine the species that is most appropriate for research on the neurobehavioral effects of Hg vapor.