Dietary sources of a -linolenic acid, such as perilla seed oil, may have the capacity to inhibit the generation of leukotrienes (LTs) by leucocytes in patients with asthma, as has been reported with the consumption of other long - chain n- 3 fatty a-cids. The factors affecting the suppression of leukotriene (LT) C4 generation by leucocytes were examined by comparing the clinical features of patients with asthma who had been given dietary perilla seed oil (n - 3 fatty acids). Group A consisted of patients in whom the leucocyte generation of dietary perilla seed oil LTC4 was suppressed by this procedure. Group B consisted of those in whom LTC4 generation was not suppressed. LTC4 generation by leucocytes significantly decreased in group A for two (P<0.05) and four weeks (P