We studied the biochemical and functional properties of semen to evidence markers of diseases concerning fertility. We examined LDH especially isoenzyme LDHx in semen of patients with varicocele, diagnosed by clinical evaluation and doppler velocimetry. The existence of this enzyme is closely associated with active spermatogenesis. In conditions of testicular disease as in varicocele, a major diffusion of LDHx into the seminal plasma may occur as a reaction of the seminiferous epithelium. We evaluated 50 patients (10 normospermic patients, 20 affected by varicocele, 9 azoospermic patients, 11 oligo-astenospermic patients). We observed that the LDHx concentration in seminal plasma is proportional to the severity of the clinical damage. The follow up after spermatic vein ligation of the patients affected by varicocele demonstrated that these patients improved to the normal clinical parameters, associated to a decrease of the concentration of LDHx values.