Rhesus monkeys (Macaca mulatta) were exposed to propylene glycol 1,2-dinitrate (PGDN) vapors on either an acute (4-h) or chronic (125-d) schedule. During acute exposures, PGDN concentrations ranged from a low of 2 ppm (parts per million) to a high of 33 ppm. Free operant avoidance behavior and visual evoked responses were monitored and free operant avoidance was not affected at any dose level. The late positive (100-150 ms) wave of the visual evoked response increased 20% at 2 ppm and decreased 25% at concentrations up to 33 ppm. Although these changes were statistically different from control values, they were within the limits caused by distracting events (+/-40%), and might possibly have been caused by the irritating or distracting properties of the vapor. Other monkeys were exposed to successively increasing concentrations of PGDN vapors at 0.3-4.2 ppm. 23 h/d, for 125 d. Daily performance testing included alternating sessions of discrete-trial cued avoidance and free operant avoidance. Non of the PGDN concentrations had a discernible effect on either type of avoidance performance.