Use of 6-desaturated n-6 fatty acids, especially gammalinolenic acid (GLA), dihomogammalinolenic acid (DGLA) or arachidonic acid (AA), together with a pharmaceutically acceptable material reducing intracellular levels of sorbitol in the body, particularly an aldose reductase inhibitor, in the treatment of (including prophylactic treatment), and in the preparation of medicaments for the treatment of (including prophylactic treatment), the long-term complications of diabetes mellitus. Pharmaceutical compositions of said materials. The ascorbate esters of 6-desaturated n-6 fatty acids (other than GLA or DGLA) per se.