Hepatic cells of chicks fed a purified basal diet consisting of isolated soybean protein (Drackett Assay Protein C-1) with no supplemental zinc, exhibited nucleoli 78% larger than nucleoli of hepatic cells in equal number of chicks fed the same diet supplemented with 40 ppm of zinc. No other histopathologic changes were observed in sections of heart, spleen, kidney and small intestine.