Linolenic acid is the unstable component of soybean [Gly- cine max (L.) Merr.] oil responsible for undesirable odors and flavors commonly associated with poor oil quality. The soybean line M-5, developed by mutagenesis from Bay, had a half of linolenic acid content compared to that of the original variety. Reciprocal crosses of both F₁ seeds and F₁ plants did not differ significantly, which indicated no maternal effect on linolenic acid content. Cytoplasmic inheritance was not observed based on the lack of reciprocal differences for linolenic acid in the analysis of both F. seeds and F2 plants. The content of linolenic acid in both F₂ seeds and plants was distributed as a trimodal pattern and the results indicated that the low, intermediate normal contents of this fatty acid were in 1 : 2 : 1 ratio. The low and intermediate linolenic acid contents in theseeds of B₁, and intermediate and normal contents in the . seeds of B₂ were fitted with the ratio of 1 : 1. These results indicated that linolenic acid in M-5 was controlled bv Materials and Methods a single major gene, acting in an additive manner. Due to the absence of maternal and cytoplasmic effects, and since a single major gene controlled the linolenic acid, the M-5 mutant could be used in a breeding program to improve the Bay (Takagi et al. 1990) was modified and renamed the variety with low linolenic acid content.