INTRODUCTION This study was initiated to determine the synergistic effects of five common air pollutants in cynomolgus monkeys (Macaca fascicularis) exposed continuously@ 24-hours per day@ seven days a week@ for a period of 104 weeks. The pollutants examined@ singly and in binary combination@ were three gases@ nitrogen dioxide@ sulfur dioxide@ and carbon monoxide and two particulates@ calcium sulfate and lead chlorobromide. The nominal exposure levels selected and the current Threshold Limit Values (1)@ presently set for each pollutant are presented in Table 10 The nominal particle size selected for the two particulates@ calcium sulfate and lead chlorobromide@ was less than two microns. This paper presents a brief overall summary of the results of measurements made on monkeys exposed singly and in binary combination to the pollutants noted above and briefly summarizes the methodology used.