"Increased fresh tomato trade has prompted a number of trade disputes between the United States, Canada, and Mexico. One precondition of an antidumping dispute is meeting the "likeness of product" criterion. However, fresh tomato shipments and imports are highly seasonal, suggesting that the degree of substitutability (or product likeness) may depend fundamentally on whether fresh tomato varieties are in- or out-of-season. We develop a seasonally adjusted inverse demand system using Canadian and Mexican monthly import data along with U.S. state shipping data to address both seasonality and product substitutability in the fresh tomato market. We find that market equilibrium and the degree of product substitution are affected by seasonality and product availability in the consumer choice set." Copyright (c) 2009 Canadian Agricultural Economics Society.