This study aims to analyze the relations of causality and price transmission of the cassava root, the cassava starch, the cassava flour, the wheat, the wheat flour and the corn, in the State of Parana. The used data goes from January 1995 to December 2005, with monthly regularity. It was applied the methodology of Granger causality to test the relations between the variables. The results showed long term relations between corn and cassava root prices, cassava starch and cassava flour prices, wheat and corn prices and wheat and wheat flour prices. It was emphasized the dependence of the cassava root prices in relation to corn, wheat, cassava starch and cassava flour prices and its little influence on these variables. It was also noted that cassava flour prices influenced the cassava starch prices, and the strong relation between the wheat prices and the wheat flour prices. The cassava flour and the wheat prices presented lesser dependence of the others variables. The paper concluded that there are important interrelations between the studied variables. The cassava root prices were the ones that depended most on the other variables in this study.