Objective: To describe the effect of varicocele, in an experimental rat model, on the levels of IL-1β and IL-1 β proteins in testis tissue. Design: Comparative and controlled study. Setting: Experimental research. Animal(s): Wistar male rats in experimental and control groups. Intervention(s): The control group underwent sham operation (n_6). Experimental groups underwent partial ligation of the renal vein to induce experimental varicocele and were then killed at 9(n_6), 11(n_6), and 13(n_6) weeks after induction of varicocele. Main Outcome Measures: Histologic evaluation of the varicocele model was determined by periodic acid-Schiff staining of paraffin-embeded testicular tissues. Levels of cytokines were assessed by mmunohistochemistry and Western blot analysis. Results: Varicocele caused testicular damage, especially in 11- and 13-week-old varicocele groups. In sham-operated rats, Golgi complexes of round spermatids expressed especially the_form of IL-1. By the progression of varicocele, the IL-1_xpression increased temporally in Sertoli cells, spermatogonia, primary spermatocytes, spermatids, and Leydig cells. The expression of IL-1_was seen in Leydig cells in shamoperated rats. The IL-1_ expression was also increased upon progression of varicocele in Leydig cells, Sertoli cells, and spermatogonia. Conclusion: We suggest that IL-1_ and IL-1_ are the regulators of testicular function. Certain pathologic conditions, e.g., varicocele, cause an increase in the expressions of such proinflammatory cytokines. The increased expression of IL-1_ and IL-1_ in varicocele shifts the balance in favor of inflammatory and immune responses and causes detrimental effects in testis tissue, which may cause male infertility.