The workplace exposure of chemicals has steadily increased, therefore the concern for subsequent effect on reproductive outcome has been an important issue in occupational medicine. In previous studies, higher rates of spontaneous abortion, reduced fertility and menstrual disorder among women, and an impairment of sperm quantity and quality among men have been associated with a wide variety of chemical agents. This study was conducted to evaluate the effects of toluene, xylene and trichloroethylene (TCE) injection on the mRNA levels of GnRH, GnRH receptor and Pit-1 genes in male rats hypothalamus and pituitary and the effects on the plasma levels of FSH, LH, prolactin and testosterone. Sprague-Dawley male rats were divided into five groups of five each according to concentration of toluene, xylene and TCE. The rats were injected subcutaneously to 0, 50, 100, 200, 400 mg/kg body weight/day of toluene, xylene and TCE, respectively for 6 days. Rat brains were excised and hypothalamus and pituitary were separated. Reverse transcription-polymerase chain reaction (RT-PCR) and RNase protection assay (RPA) were used to evaluate the GnRH, GnRH receptor and Pit-1 mRNA levels. Plasma concentrations of FSH, LH, prolactin and testosterone were assayed by radioimulunoassay (RIA). The results were as follows; 1. GnRH, GnRH receptor and Pit-1 mRNA levels in toluene and xylene injected groups, and GnRH receptor mRNA levels in TCE injected group were lowered dose-dependently. Especially, GnRH receptor and Pit-1 mRNA levels in 200 mg/kg of toluene injected group, and GnRH, GnRH receptor and Pit-1 mRNA levels in 400 mg/kg of toluene injected group were significantly lowed than control group (p<0.05). GnRH receptor and Pit-1 mRNA levels in 400 mg/kg of xylene injected group, and GnRH receptor mRNA levels in 400 mg/kg of TCE injected group were significantly lower than control group (p<0.05). 2. The plasma levels of prolactin and testosterone in 400 mg/kg of toluene injected group, and LH in 100, 200 and 400 mg/kg of xylene injected group, and testosterone in 400 mg/kg of TCE injected group were significantly lower than control group (p<0.05). In conclusion, we speculated that toluene and xylene affected reproductive system secondarily through hypothalamus-pituitary axis, and TCE affected directly through steroidogenesis. And we recomended that further study for assessment of the reproductive toxiclty of mixed organic solvent exposures should be conducted.