Activities of total lactate dehydrogenase, which plays an important role in providing energy for cell metabolism, lactate dehydrogenase-X, an isoenzyme of lactate dehydrogenase supposed to be specific for germinal epithelium activity, diluted semen absorbance and some other properties have been measured in 51 seminal plasma samples. Aiming to study its clinical use as a marker of seminiferous epithelium activity, determination of isoenzyme-X and investigation of correlation between it and the spermiogram properties were carried out. Besides lactate dehydrogenase and lactate dehydrogenase-X activity, their ratio and diluted semen absorbance were correlated with the different properties of the spermiogram, the best correlation of the enzymes being obtained with the total sperm count and motile sperm count. Correlation of diluted semen absorbance with the total sperm count and motile sperm count was also noted, whereas it did not correlate with sperm concentration and motility rate. The data suggests the clinical utility of these properties as reliable markers for both germinal activity and spermatozoid quality when ''total sperm count'' and ''motile sperm count'' are used to define sperm properties instead of just sperm concentration and motility rate.