en Clinical Biochemistry Clinical Biochemistry Original Research: Clinical Science Original Research: Clinical Science Background: The lipid peroxides and their degradation products are highly toxic to spermatozoa and may play a major role in sperm dysfunction. The purpose of this study was to determine the level of lipid peroxidation as indicated by malondialdehyde (MDA) in the spermatozoa and seminal plasma of asthenozoospermic and normozoospermic males. In addition, correlation of lipid peroxidation with motility grades: a (rapid progressive), b (slow progressive), c (nonprogressive ), d (immotile ), percent of normal morphology, acrosome and tail defect, and concentration of spermatozoa was determined. Methods: MDA of spermatozoa and seminal plasma was determined in 35 asthenozoospermic and 15 normozoospermic men by spectrofluorometry. Semen analysis was done according to the WHO standard. Results: MDA in the spermatozoa of asthenozoospermic patients was significantly higher than normozoospermic males (0.14±0.0 1 and 0.09±0.0 1 nmol/1 0* 106 spermatozoa respectively, mean ±SE). A significant negative correlation was observed between MDA of spermatozoa with grade a motility and concentration of spermatozoa. In addition, a significant positive correlation was observed between MDA of spermatozoa with the acrosome and tail defect. The MDA value in the seminal plasma of asthenozoospermic and normozoospermic patients was 1.35±0.07 and 1.2±0.08 nmol/mL seminal plasma respectively (mean±SE). The MDA of seminal plasma exhibited a negative correlation with grade a+b motility and positive correlation with grade c+d motility and head defect. Conclusion: Lipid peroxidation has a deleterious effect on semen quality and MDA is an index of lipid peroxidation which may be a diagnostic tool for the analysis of infertility in asthenozoospermic patients. Asthenozoospermia, Lipid peroxidation, Semen Parameters, Human Spermatozoa, Semen Analysis. 339 344 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-23&slc_lang=en&sid=1 HEIDAR TAVILANI 20031947532846003288 20031947532846003288 No MAHMOUD DOOSTI doostimd@sina.tums.ac.ir 20031947532846003289 20031947532846003289 Yes Department of Medical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences HOJATOLLAH SAEIDI 20031947532846003290 20031947532846003290 No SEYED MOHAMMAD HOSSEINIPANAH 20031947532846003291 20031947532846003291 No HASAN HASANI BAFERANI 20031947532846003292 20031947532846003292 No