Abstract: The invention is concerned with the use of certain fatty acids and inhibitors of an enzyme in effecting modifications to the lipid structure of cell membranes. The invention also relates to the formulation of pharmaceutical compositions and medicaments and to such products per se; to the treatment of a variety of clinical and veterinary disorders associated with a lowering of the saturation index of cell membranes, including malignancies, viral disorders and AIDS; and to the use of the active materials of the invention in the relief of pain.The active principals in the present invention are saturated fatty acids having from 12 to 28 carbon atoms in the alkyl chain, e.g. stearic acid, or pharmaceutically acceptable derivatives thereof; and inhibitors of the enzyme .DELTA.-9 desaturase, e.g. sterculic acid and malvalic acid or pharmacologically active derivatives or analogues thereof.