3-hydroxy-2-phenylcinchoninic acid (also known as oxycinchophen or earlier as HPC) was known as antidiuretic and has been specially found useful in cases of diabetes insipidus. Clinical studies of HPC revealed that this compound reduces water output in cases of diabetes insipidus, and this was reached not by direct action on the water reabsorbing element in the tubules of the kidney, but rather by the mediation of HPC on the pituitary system in the production of the antidiuretic hormone therein. The effect of HPC upon fever and arthritis on patients with rheumatic fever was dramatic. In addition, HPC cannot be considered as an antipyretic, but rather HPC should be considered as enhancing ins some way the output or activity of adrenal cortical hormones. HPC was shown rather toxic (toxic reaction were presented in 20 % of tested patients). That is why the development of this drug was stopped and is become study its derivatives.