Background, Aims and Method:  2,5-Hexanedione is an industrial solvent which causes peripheral neuropathy. In the current study, the effect of 2,5-hexanedione on testicular histology of adult rats as well as sperm concentration, motility, and morphology were studied by administering 100 mg, 200 mg, 400 mg/kg per day for 12 weeks. Results:  No sperm motility was observed in the 200 mg and 400 mg/kg per day treatment groups and significantly reduced motility was observed in the 100 mg/kg per day group. The morphology were also significantly reduced in the 200 mg and 400 mg/kg per day groups compared to the control group, but the sperm concentration was significantly reduced only in the 400 mg/kg per day group. Histological examination of the testes in the 400 mg/kg per day group revealed that two-thirds of the testes had Sertoli cell only syndrome, whereas in the 200 mg/kg per day group half of the testes showed maturation arrest and sperm as well as spermatids were observed in 83% of the testes. Conclusions:  In conclusion, we have shown that 2,5-hexanedione severely affected sperm motility even at low doses, whereas high doses adversely affected all the sperm parameters as well as causing testicular injury. (Reprod Med Biol 2004; 3: 59-62).