It is well known that during space flight the constant influence of weightlessness leads to several modifications of many cellular physiological processes such as proliferation, differentiation, growth, signal transduction, cytoskeleton, motility and gene expression. Our several experiments in real and simulated microgravity showed that T cell proliferation is reduced more than 90% and that IL-2 and IL-2-R-alfa receptor expression, LFA-1 and ICAM-1 adhesion proteins are involved, also cytoskeleton pattern and monocyte motility undergoes intense modifications. The aim of this research is to investigate the effects of microgravity on the immune system using proteomics approach. This preliminary work constitutes a comprehensive study of tyrosine and serine phosphorylative changes in Jurkat cell membrane proteins, performing a differential analysis by 1-DE and 2-DE separation. The identification of phosphorylated residues by LC-MS-MS evidenced the inadequate protein separation by 1-DE, so we decided to better separate Jurkat cell proteins by 2-DE. Western blot with anti-phosphotyrosine and anti-phosphoserine antibodies revealed to be very sensitive and accurate, Jurkat cell proteins are extensively modified after Con A treatment at different incubation times. Although the observed modifications could play a central role in a large number of processes, additional knowledge is clearly required to consider the functional consequences of the protein modifications described in the present report.