An intense peak is visible in the phosphodiester region of the 31P NMR spectra of human colon adenocarcinoma HCT-8R cells. A signal at the same frequency, partially deriving from mobile phospholipids, is also observable in the spectra of total membranes and of perchloric acid extracts prepared from the same cells. The phosphodiester signals of glycerophosphorylcholine, glycerophosphorylethanolamine, and glycerophosphorylserine resonate at lower fields with respect to this broader peak and appear only in aged samples. Enzymatic treatments of the extracts would indicate that ribonucleic acid also contributes to the broad phosphodiester signal. Moreover, 1H NMR spectra show the presence of lipid structures, characterized by high mobility, in the cell and in the membrane samples, similar to what was already observed in other tumor cells and tissues.