The effects of ethylene glycol monoethyl ether (EGEE) on testicular cell populations in pubertal (5 weeks old) and adult (9 weeks old) male rats were investigated by a flow cytometric method. A total of 50 rats (in number, 25 pubertal and 25 adult rats) was divided into 5 experimental groups including 0 (control), 50, 100, 200, and 400 mg EGEE/kg of body weight. The animals were administered by gavage for 4 weeks. In adult rats, the treatment of EGEE at the dose of 400 mg/kg of body weight decreased significantly the populations of haploid, while it increased those of diploid and tetraploid cells. In pubertal rats, the treatment of EGEE at the dose of 400 mg/kg of body weight caused only minimal changes in the relative percent of testicular cell types. These results suggest that the effects of EGEE on testicular function in pubertal rats appear to be less pronounced than in adult rats.