The uptake of isotope by 3 transplanted kidney tumors after i.p. injection of 3H-labeled orotate was 5% of that in the host kidney cortex. A decrease of similar magnitude in uptake into the acid-soluble tissue fractions from kidney tumors was observed with low incorporation into RNA relative to the host kidney cortex. Total uptake of orotate-3H and incorporation into RNA were several fold higher in the normal kidney cortex. Total uptake of orotate-3H and incorporation into RNA were several fold higher in the normal kidney cortex than in the kidney medulla and for the kidney cortex both parameters were less in young than in old rats. The uptake of uracil-3H by 2 kidney tumors was .apprx. 40% of that in the kidney cortex of host rats. Although the uptake of orotate-3H in kidney cortex was greater than that for uracil-3H the reverse situation was observed with kidney tumors, indicating that renal neoplasia in the rat is accompanied by an altered pattern of uptake of these metabolites.