BACKGROUND It has been observed that the use of immunosuppressive drugs in patients after transplantation of vascularized organs may be associated with changes in the concentration of certain fractions of plasma proteins. The concentration of these proteins was correlated with an increased risk of occurrence of stage 3 chronic kidney disease (CKD). This article examines the effect of the most commonly used immunosuppressive drugs on the concentration of plasma proteins in Wistar rats. MATERIAL AND METHODS The study involved 36 rats grouped according to the immunosuppressive regimen used (tacrolimus, mycophenolate mofetil, cyclosporine A, rapamycin, and prednisone). The rats in all study groups were treated with a 3-drug protocol for 6 months. The treatment dose was adjusted based on available data in the literature. No drugs were administered to the control group. The rats were sacrificed and blood samples collected to determine the concentration of plasma proteins using electrophoresis technique. RESULTS Statistically significant differences were observed between protein concentrations within the studied groups. The differences related to the proteins with masses of 195 kDa, 170 kDa, 103 kDa, and 58 kDa. CONCLUSIONS (1) Immunosuppressive drugs caused changes in the proteinogram of plasma proteins. (2) The strongest effect on rat plasma proteins was exerted by a regimen based on rapamycin. Intermediate, weak, and weakest effects were observed in regimens based on cyclosporine A, tacrolimus, and mycophenolate mofetil, respectively.