To investigate whether testosterone, estrogens, vasectomy, experimental cryptorchidism, varicocele or aging would induce changes in the cytokine environment of the mouse testis. Methods: In adult male BALB/c mice,testosterone implants, estradiol benzoate, vasectomy, unilateral cryptorchidism, unilateral varicocele were adminis tered/performed. The mice were followed up for different periods of time and were then sacrificed with testes incised for examination. The control mice received the vehicle or sham-operation. Results: IL-10 was present in Leydig cells of nearly every testis and IL-10 + macrophages in 39% of testes. IL-6 was found in the testes of intact adult mice, mice treated with testosterone for 70 days, cryptorchid testes and sham-operated testes. Conclusion: Results suggest that IL-10 might be involved in the generation of the immunologically privileged microenvironment in the testis.