The nutritional values of raw grain, nixtamal and tortillas from maize, whole sorghum and pearled sorghum were determined with weanling rats and with three in vitro assays. Dry matter and gross energy digestibilities of pearled sorghum products were highest ( P < 0·05) followed by the maize and whole sorghum products. Nixtamal and tortilla processing slightly increased dry matter and gross energy digestibilities ( P < 0·01) for maize and whole sorghum but not for pearled sorghum ( P>0·05). Apparent protein digestibility of maize, whole sorghum and pearled sorghum products slightly decreased ( P < 0·05) with processing. Apparent protein digestibilities of pearled sorghum nixtamal and tortillas were significantly higher ( P < 0·05) than maize nixtamal and tortillas and both were higher ( P < 0·05) than whole sorghum. Rats fed maize and whole sorghum nixtamal and tortilla had poorer ( P < 0·05) feed/gain ratio than rats fed raw grains. Rats fed raw pearled sorghum had similar feed/grain ratio to rats fed pearled sorghum nixtamal or tortillas. Pearled sorghum feed/gain values were worse because decortication removed 14·3 % of the limiting amino acid, lysine. In vitro protein digestibility results indicated that the multiple enzyme pH-stat procedure correlated better with the in vivo apparent protein digestibilities than did systems containing the pronase and pepsin in vitro. It is concluded that the substitution of sorghum for all or part of the maize in tortillas should not seriously affect their nutritional value.