This chapter describes a method for qualitative detection of complement activation by western blot. This method uses the cleavage product of the C3 component as a marker for complement activation by any pathway. In this protocol, human plasma is exposed to nanoparticles and then analyzed by polyacrylamide gel electrophoresis (PAGE) followed by western blot with anti-C3-specific antibodies. These antibodies recognize both the native C3 component of complement and its cleavage products. The amounts of C3 and the C3 cleavage products are compared to the amounts in control (untreated) plasma and to plasma treated with a positive control to provide a quick and inexpensive qualitative assessment of complement activation.