The effect of recombinant glycodelin (GdA) on the number of T-regulatory lymphocytes (Treg) in a culture of activated CD4+ lymphocytes was investigated, while simultaneously assessing the proliferative status of the cells. Recombinant GdA from E. coli and from HEK293 cells were used in the study at concentrations of 0.2; 2 and 10 µg/mL. It was found that only a low concentration (0.2 μg/mL) of recombinant GdA of bacterial origin reduced the number of proliferating CD4+ lymphocytes as well as the number of Treg (CD4+CD25highCD127-/low) in the experimental system in vitro.