Abstract
Rats were injected 4 times with 100 ug. aminopterin during 68 hrs., followed by 10 n moles of C14 formate. Nineteen hrs. after formate injn. the intestinal ribonucleic acid showed a small reduction in specific activity when compared with control animals not treated with aminopterin. In contrast, liver ribonucleic acid and ribonucleic acid purines of the treated animals showed an approx. 15-fold increase in specific activity over controls.