In recent years, it has been noted that there is a close correlation between leukotrienes and late asthmatic reaction (LAR). In this study, effects of dietary supplementation with perilla seed oil rich in alpha-linolenic acid, which is speculated to affect the generation of leukotrienes through metabolism of arachidonic acid (AA), were evaluated in 6 patients with asthma. The symptoms and ventilatory function were improved after 2-week dietary supplementation with perilla seed oil. The generation of LTB4 and LTC4 by peripheral leucocytes stimulated with Ca ionophore A23187 was significantly suppressed by the dietary supplementation (LTB4 and LTC4 ; p<0.05). Regarding the composition of fatty acids in serum phospholipids, the concentrations of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and AA tended to increase after the supplementation, accompanied with an increase in the ratio of EPA to AA. These results suggest that dietary supplementation with perilla seed oil brings beneficial effects in the treatment of asthma.