Low testicular volume (TV) is associated with a decreased testicular function. Several studies explored the conventional sperm parameters and the endocrine function in patients with low TV. No other parameters have been examined. On the basis of these premises, the aim of this study was to evaluate a non-conventional seminal parameter: seminal lymphocyte characterisation in men with low TV compared with that of subjects with normal TV. A further comparison was made between fertile men and infertile patients with low or normal TV (78 patients). The testis was considered normal in size when it had a volume between 15 and 25 crrr', low-normal with a volume between 10 and 12 em" and hypotrophic when the volume was <10 cnr'. Statistically significant differences were observed in the following sperm parameters: percentage of immature germ elements, peroxidase-positive leukocyte concentration and CD45pos leukocytes (p<0.05). A correlation analysis showed the presence of a positive linear relationship between CD45pos leukocytes and the percentage of immature germ elements (r=0.88; p<0.05) and between CD45pos leukocytes and the percentage of spermatozoa with phosphatidylserine externalisation (r=0.90; p<0.05) as well as a negative linear relationship between the percentage of spermatozoa with normal morphology and the seminal CD45pos leukocyte concentration (r=-0.75; p<0.05). The results of this study showed that patients with low testicular volume «10 em') have a significantly increased CD45pos concentration that is associated with increased percentages of immature germ elements, spermatozoa with signs of early apoptosis, and spermatozoa with abnormal morphology.The testis is an oval-shaped organ that, in adult men, weighs approximately 20 g, has an average volume (TV) of 18.6±4.8 em' and dimensions ranging from 3.6 to 5.5 em in length and 2.1 to 3.5 ern in width. Within the testis, there are approximately 400-600 seminiferous tubules that are 70-80 em long and have a diameter of 0.12-0.13 mm, representing 80-90% of the total testicular volume (1). The testis consists of two structurally distinct compartments: the interstitial cell or Leydig cell compartment and the seminiferous tubule compartment, which contains germ cells and Sertoli cells. These two compartments are responsible for the two main testicular actions: the endocrine and the exocrine function (production of androgens and spermatozoa). In the clinical practice, TV can be estimated by a physical examination using an orchidometer, but it can be more objectively assessed by an ultrasound examination, which is less affected by factors such as scrotal effusions, varicose veins, intra-scrotal masses, testicular pain, and distinction with the adjacent anatomical structures (2). It has