Objective To explore the changes of serum male hormone, androgen binding protein (ABP) expression as well as the proliferation of testicular cells in rats with experimen- tal orchitis induced by bacterial lipoplysaccharide (LPS) in vivo and to elucidate the putative mechanism of LPS on spermatogenesis of testis. Methods The serum testosterone (T), luteinizing hormone (LH) levels were detected with magnetic enzyme immunoassay. The expression of proliferating cell nuclear antigen (PCNA) and ABP expression at mRNA level of testis were studied with immuno- histochemical staining and in situ hybrydization respectively. Results The serum T level in rats with experimental orchitis was significantly higher than that in the rats of control (P<0.05) and ABP mRNA expression in Sertoli cells of testis was significantly increased (P<0.05) while PCNA expression in seminiferous epithelium in experimental rats significantly was decreased as compared with that of the control (P<0.05). No significant change in serum LH level was seen between ex- perimental orchitis and control groups (P>0.05). Conclusion The serum level of T and ABP expression significantly increased in rats with experimental aspecific orchitis induced by LPS, and at the same time inhibition of cellular proliferation of seminiferous epithelium can be detected, which may be the possible mechanism of male infertility in inflammatory process. Objective To explore the changes of serum male hormone, androgen binding protein (ABP) expression as well as the proliferation of testicular cells in rats with experimen- tal orchitis induced by bacterial lipoplysaccharide (LPS) in vivo and to elucidate the putative mechanism of LPS on spermatogenesis of testis. Methods The serum testosterone (T), luteinizing hormone (LH) levels were detected with magnetic enzyme immunoassay. The expression of proliferating cell nuclear antigen (PCNA) and ABP expression at mRNA level of testis were studied with immuno- histochemical staining Results of the serum T level in rats with experimental orchitis was significantly higher than that in the rats of control (P <0.05) and ABP mRNA expression in Sertoli cells of testis was significantly increased (P <0.05) while PCNA expression in seminiferous epithelium in experimental rats significantly decreased decreased as compared with that of the control (P <0.05). No significant ch ange in serum LH level was seen between ex- perimental orchitis and control groups (P> 0.05). Conclusion The serum level of T and ABP expression significantly increased in rats with experimental aspecific orchitis induced by LPS, and at the same time inhibition of cellular proliferation of seminiferous epithelium can be detected, which may be the possible mechanism of male infertility in inflammatory process.