To investigate the expression of RhoGDIalpha in human testes and spermatozoa, and compare the expression of RhoGDIalpha in the ejaculated spermatozoa from normozoospermic me and infertile patients men receiving in vitro fertilization (IVF).The localization of RhoGDIalpha in the human testis was determined by immunohistochemistry, and that in the pre-capacitated, capacitated and acrosome-reacted sperm by immunofluorescence. Western blot was used to detect the expression of RhoGDIalpha in the semen samples obtained from normozoospermic males (n = 10), IVF patients with high fertilization rates (> or = 60%, n = 12) and those with low fertilization rates (< 60%, n = 13).Immunohistochemistry showed that the RhoGDIalpha protein was located in all spermatogenic cells and highly expressed in the elongated spermatids. Immunofluorescence exhibited a high expression of RhoGDIalpha in the acrosome and flagellum of human sperm, which decreased in the acrosome after capacitation and disappeared after acrosome reaction. Western blot revealed an obviously decreased expression of RhoGDIalpha in the spermatozoa of the IVF patients with low fertilization rates (0.66 +/- 0.18), with statistically significant difference from those with high fertilization rates (0.97 +/- 0.17) and the normozoospermic men (1.13 +/- 0.21).The RhoGDIalpha protein is located in the acrosome and flagellum of human sperm, and might be involved in sperm movement, capacitation and acrosome reaction. The significantly reduced expression of RhoGDIalpha in the sperm of low-fertilization patients suggests that it may be a new diagnostic biomarker for male infertility, and has a potential application value in sperm selection for IVF.