When to 20 mgm. adenylic acid from muscle tissue, dissolved in 1 cc. water with 1 drop of 10% NaOH, 6 drops CuSO4.5 H2O (2% solution) are added, a clear blue soln. results; after 6 drops more of the Cu salt a precipitate appears, which is dissolved by 3 drops 1% NaOH. Adenosine gives the same reaction. When adenine nucleotide from yeast nucleic acid is treated in the same way only a precipitate of Cu(OH)2 and a colorless soln. result, even when 6 drops more of 10% NaOH are added.; only after 13 drops of 30% NaOH was a blue solution obtained; but water, CuSO4, and NaOH also give such a blue solution. Guanylic acid from pancreas and from yeast nucleic acid reacts like adenine nucleotide from yeast nucleic acid. The objections of Steudel (Hoppe-Seyler''s Z. physiol. Chem., 216, 77, 1933) against the reaction of Klimek and Parnas are explained by this author''s mistake of taking too much NaOH. It was reported by Steudel (Z. physiol. Chem., 211, 255, 1933) that he was not able to isolate adenylic acid from fresh beef muscle, and since this has not previously been re-ported by any other author the preparation of adenylic acid was tried with quite fresh beef. 5.8 gm. were obtained from 30 kgm. meat.