The effect of all-trans-retinol on tumor cell line HCT-8R from human colon adenocarcinoma has been examined. Growth inhibition in the absence of cytotoxic effect has been observed. T1 and T2 relaxation times of 1H NMR resonances from mobile lipid domains are shortened by adding the vitamin A to the culture medium. Furthermore, the 31P NMR phosphodiester signal, attributed to a RNA-proteolipid complex from plasma membrane, is affected by retinol treatment. A possible correlation between growth inhibition and NMR results is discussed.