The discovery, tissue distribution, concentration in extracellular fluids and structure of human gamma-trace are reported. The use of determinations of the cerebrospinal fluid concentration of gamma-trace in the diagnosis of hereditary cerebral hemorrhage with gamma-trace-amyloidosis is described. The physiological function of gamma-trace as a cysteine proteinase inhibitor is accounted for an it is suggested that the six trivial names used for gamma-trace so far are replaced by the functional designation cystatin C.