✓ Three cases of shunt nephritis in which serial complement levels were obtained during the course of treatment are presented to illustrate the value of monitoring complement levels in the management of this condition. In shunt nephritis, circulating immune complexes are formed which contain antigen from bacteria of low virulence. These complexes, which activate the classical complement pathway, are reflected in most cases by lowering of the serum levels of C1, C2, C4, and C3. These levels promptly return to normal after the initiation of effective therapy. Serial determinations of serum levels of complement protein provide a sensitive and reliable method for early determination of efficacy of therapy in shunt nephritis.