In this study, we investigated the effects of polychlorinated biphenyls (PCBs) and organochlorinated pesticides on the serum levels of luteinising hormone (LH), follicle stimulating hormone (FSH) and weights and histomorphometry of uterine tissue in immature female rats using uterotrophic assay. A total of 36 rats were randomly divided into six groups ( n = 6 per group) as control, oestradiol (E₂, 100 μg/kg), PCB 180, Aroclor 1221, endosulfan and mirex at 10 mg/kg dosage. After 3 days of injections (subcutaneous), animals were decapitated and blood samples were collected. Uteri were dissected, weighed out and then fixed in 10% formaldehyde. They were processed for histomorphometry. The serum levels of LH and FSH were determined by enzyme immunoassay. Uterine weight was significantly increased by E₂ and reduced by mirex ( p < 0.001 and p < 0.05, respectively). Total volume of uterus was significantly raised by E₂, Aroclor 1221 and endosulfan compared with that of the control group ( p < 0.01). The ratio of epithelium was significantly increased by E₂, PCBs and pesticides ( p < 0.01). The uterine cavity ratio was decreased by aroclor ( p < 0.01), PCB 180 and mirex ( p < 0.05). The serum levels of LH did not significantly differ among the groups but the levels of FSH were decreased by PCB 180 and endosulfan ( p < 0.05 and p < 0.01, respectively). These findings suggest that PCB 180, Aroclor 1221 and endosulfan may be estrogenic in immature uterotrophic assay.