Utilizing a simple, rapid, and inexpensive modification of a fluorometric method, we determined the normal concentrations of nucleic acids (DNA and RNA) in human blood plasma of healthy individuals. DNA concentrations (13.9 ± 3.7 mg/ liter) were in excellent agreement with those reported by other methods. However, the RNA concentrations (144 ± 22 mg/liter) we found were higher than previously reported values, possibly because ribonuclease activity is more inhibited in this fluorometric method.