INTRODUCTION This study was initiated to determined 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 (TLV) (1) presently set for each pollutant are presented in Table 1. The nominal particle size selected for the two particulates@ calcium sulfate and lead chlorobromide@ was less than two microns (lt;2??. This report presents the results of measurements made on monkeys exposed to carbon monoxide singly and in binary combination with nitrogen dioxide@ sulfur dioxide@ and lead chlorobromide and briefly summarizes the methodology used. A series of technical reports have been issued describing the methodology in detail; these are listed in Table 2.