Reiber's quotient diagram or reibergram has a growing apply for characterize the intratecal synthesis of proteins. Firstly reibergrama was used for the major classes of immunoglobulins but later it was used to evaluate other proteins based on the theory about molecular flux/cerebrospinal fluid (CSF) flow rate.C3c is a degradation product of complement factor C3 with 145 KDa and approaches to IgG molecular characteristics according with Fick's diffusion laws. It was assumed IgG constants and graphic for IgG constants and graphic to evaluate the intrathecal synthesis of C3c. Twenty-seven patients and 27 controls were studied. Serum and CSF C3c and albumin were quantified by immunodiffusion.The patients with the C3c proposed reibergram were evaluated. It has been proved its validity under several CSF blood barrier conditions.Reibergram for C3c can be used for the evaluation of the intrathecal synthesis of this protein.