For years we have puzzled over the meaning of a slight increase in the value of serum bilirubin, with or without slight jaundice, barely detectable either by the patient or by the trained physician. Naturally we have suspected that in at least some of these cases the liver has suffered an injury leading to dysfunction, but we could not be sure. In the hope of throwing light on the problem, we have analyzed the data in all such cases encountered at the Mayo Clinic from 1930 to 1931. It will be remembered that in most laboratories today the concentration of serum bilirubin is classified and measured by van den Bergh's technic. At the clinic, Lepehne's ring test is first applied to determine the type of bilirubin reaction. If, after the diazo-reagent has been added, a purple color appears within one minute, the reaction is said to be "direct;" if the