C4d is a surface-bound split product of C4b that can serve as marker for activation of the classic and lectin pathways of complement.1 C4 glomerulopathy is characterized by bright staining for C4d and the absence of staining for immunoglobulins, C1q, and C3.2,3 In the series of immunoglobulin A nephropathy by Espinosa et al,4 the C4d staining likely represented activation of the lectin pathway of complement. Similarly, in our series of C4 glomerulopathy, the C4d staining is probably due to lectin pathway activation.