The aim of the study was to assess the fatty acids profile in phospholipid fractions, in patients after heart or kidney transplantation, depending on: the type of immunosuppressive drug, transplanted organ, metabolic disorders and kidney function. The doctoral dissertation consists of four scientific publications. The review article, contains information about the type and role of fatty acids. The study included: 23 heart transplant patients (9 treated with cyclosporine (CsA), 14 treated with tacrolimus (Tac)) and 65 kidney transplant recipients (24 treated with CsA, 41 treated with Tac). The study also included 25 healthy, non-transplanted individuals who set up control groups. The concentration of fatty acids was determined by gas chromatography. The obtained results confirm that the fatty acid profile of patients after transplantation is different than in healthy people. In addition, in patients after heart transplantation, the fatty acid profile depends on the type of immunosuppressant used. In kidney transplant patients, treated with Tac, with hyperlipidaemia, the metabolism of saturated fatty acids and n-6 acids is different than in patients without metabolic disorders. In turn, the analysis of the correlation between fatty acid concentration and eGFR, showed that fatty acids are essential for normal kidney function, and their role depends on the type of fatty acid.