1. The effect of riboflavine deficiency on liver ribonuclease activity, RNA and DNA content, and 32P incorporation into RNA and DNA has been studied in rats maintained on a 16% protein diet, a protein-free diet and on a protein-free diet subsequently replaced with a 40% protein diet.
2. Rats maintained on a riboflavine-deficient diet for 45 days showed decreased incorporation of 32P into liver RNA but no effect on the RNA content of liver. The concentration of DNA in liver and 33P incorporation into it remained unaffected. After a deficiency period of 70 days, both the RNA and DNA contents of liver were found to be decreased. When the riboflavine-deficient or control rats were given the protein diet for 30 days and then a proteinfree diet for 15 days, the RNA content of their livers decreased, while the liver DNA content was increased. Repletion with a 40% protein diet restored the RNA and DNA content in both control and riboflavine-deficient rats.
3. Liver ribonuclease activity was decreased after a deficiency period of 45 days, whereas it was increased after a deficiency period of 70 days.
4. A correlation between liver RNA level and liver ribonuclease activity in riboflavine deficiency is suggested.