Dietary supplementation with perilla seed oil, a vegetable oil rich in α -lin- olenic acid, inhibits the generation of leukotrienes(LTs) by leucocytes in patients with bronchial asthma. We examined the factors that affect the suppression of LT generation by leucocytes with perilla seed oil-rich supplementation in patients with asthma, by comparing the clinical features of patients with asthma, whose generation of leukotriene (LT) C4 was suppressed by dietary supplementation with perilla seed oil (n-3 fatty acids) (group A), with those of patients who showed no suppression of LTC4 generation (group B). Group A showed a significant increase in the generation of LTB4 and L TC4 by leucocytes after corn oil-rich supplementation (n-6 fatty acids), and a significant decrease in the generation of LTB4 and LTC4 after perilla seed oil-rich supplementation (n-3 fatty acid). However, this was not observed in group B. The level of serum IgE and peak expiratory flow (PEF) in group A were significantly higher
than in group B. Furthermore, the serum levels of LDL-cholesterol, β-lipoprotein and phospholipid were significantly lower in group A than in group B. These results suggest that the clinical features differ between these two asthmatic populations with respect to suppression of LTB4 and LTC4 generation by n-3 fatty acids in perilla seed oil-rich supplementation.