The behavioral, physiologic, and pathologic effects of cyanogen (460195) inhalation were studied in male rhesus-monkeys and male Charles-River-rats. Three test groups, consisting of 5 monkeys and 30 rats each, received 0, 11, or 25 parts per million (ppm) cyanogen in exposure chambers 6 hours a day, 5 days a week, for 6 months. Monkeys participated in behavioral tests involving lever pressing activity on a variable interval schedule of reinforcement; these tests were run daily after exposure and continued for 4 weeks after cessation of exposure. Electrocardiograms were taken prior to exposure and immediately following the last exposure session. Hematocrit values and hemoglobin concentrations were determined regularly over the course of exposure. At selected intervals, animals were sacrificed for gross pathologic and histopathologic examination of organs and tissues. At the outset of exposures, there was a doubling of the rate of responding in the lever pressing task in monkeys exposed to 25ppm cyanogen, and increases were also seen in the monkeys receiving 11ppm exposures. However, these increases were transitory, and the response rate returned to normal prior to the termination of a 6 month exposure period. No effects in hematologic parameters were observed, and no changes in electrocardiograms or pathologic findings were seen. Total lung moisture content was lower in monkeys exposed to cyanogen at either concentration than in controls, and body weights were lower in rats exposed to 25ppm than in controls. The authors conclude that subchronic 25ppm exposures are marginally toxic.