In the past we have contributed to characterize the changes in nuclear protein composition, structure and expression in spermatogenesis. More recently we have contributed to identify changes in nuclear protein content of the spermatozoa and have identified different genetic defects associated to  male infertility. However, at present, the majority of causes of male infertility still remain unknown. This is partly due to the relative lack of knowledge concerning the protein composition of the spermatozoa. We have recently undertaken different proteomic projects to characterize the proteins of the sperm cells through mass spectrometry (2D -MS/MS or LC-MS/MS) both in the normal human spermatozoa,  with a particular focus on the nuclear proteins, and in infertile patients. The project is being completed with the sequencing of the promoter and coding regions of the genes corresponding to the proteins identified with a differential expression, in search for possible mutations. Additionally, the use of antibodies to proteins identified is allowing to characterize its expression providing both, basic information and a potential opportunity to be become diagnostic tools in infertility.