This study was conducted for the American Petroleum Institute to evaluate the effects of mixed xylenes on the reproductive performance of rats. Test material was administered by chamber inhalation. The target exposure levels of 0, 60, 250, and 500 parts per million (ppm, v/v in air) were achieved as follows: 0, 60, (+2 or -2), 250, (+5 or -5), and 500 (+13 or -13) ppm (+ or - Std. Dev.). These Miran determined values were within 10% of the nominal concentration and values confirmed by a secondary assay - gas chromatography. Animals (CD(trade name) rats) were treated daily (6 hrs./day) during a 131-day pre-mating period and 20-day mating period. Mated females continued to be treated daily during the Day 1-20 gestation interval and females that delivered litters were treated daily during the Day 5-20 lactation interval. The study involved six groups of animals; Group I was a chamber-exposed (sham-air) control containing 30 males and 60 females; Groups II and III were the 60 and 250 ppm dose groups and each contained 10 males and 20 females. There were three high-dose groups (500 ppm); Group IV contained 20 males and 40 females and both sexes were treated; Group V contained 10 males and 20 females but only the males were treated; and Group VI contained 10 males 20 females but only the females were treated. The untreated females in Group V and untreated males in Group VI were chambered with the Group I control animals during the treatment periods. Reproductive performance was evaluated through mating performance and pregnancy data.