Japan's policies and import demand structures for beef, maize, and sorghum were reviewed and quantified using a system of 12 seemingly unrelated equations consisting of 12 endogenous and 23 exogenous vanables. Empirical implications drawn from this model indicated that Japan's beef import quota is one of the significant factoIS that determine Japan's total beef imports and countries of origin. Hence, by the large country assumption, Japan could benefit from its protectionist beef import policy. The model also confirmed that price competition existed between Australian and New Zealand beef of identical quality and that US beef substitutes for beef from Oceania, due to quotas. The ex ante simulations showed a trade-off between beef and feed grain imports in addition to potential cross substitution of similar commodities from different sources of supply and from such close substitutes as maize and sorghum. The USA dominated the maize and sorghum trade because its exports of those commodities to Japan dominated Japan's demand functions for the commodities from other sources. For feed grain trade, the freight rates between the US Gulf ports and Japan influenced neither Thailand-Japan maize trade nor Australia-Japan sorghum trade. Australia's exportable supply of sorghum influenced both US-Japan and Australia-Japan trade in sorghum, which in tum influenced sorghum trade between Argentina and Japan.