We have studied the effect of a gamma-linolenic acid (18:3 n-6, GLA)-supplemented diet on the growth of a human lung mucoepidermoid carcinoma (HLMC) implanted in athymic mice and on its uptake of human low density lipoproteins labeled with 99mTc (99mTc-LDL). Mice bearing the HLMC were divided into two experimental groups. One of them was administered a control diet (C diet) and the other one was given a diet supplemented with 25 mg GLA/g pellet (GLA diet) for three weeks (Table 1). A tumor growth inhibition with the GLA diet was evident at the second week of treatment, and a marked inhibition (56%) was reached at the end of the third week (Fig. 1). The GLA diet produced some changes in the total fatty acid composition of tumor, plasma and liver of host mice: GLA and arachidonic acid (20:4 n-6, AA) induced significant increases, whereas oleic (18:1 n-9, OA) and linoleic acids (18:2 n-6, LA) were decreased (Table 2). Tumors of those animals fed both diets were labeled by 99mTc-LDL, and no difference was observed in the ratio of tumor/liver and tumor/kidney uptake of host animal (Table 3). Results obtained using this experimental model suggest that the inhibitory effect of GLA on tumor growth is not related to the LDL tumor uptake.