The results of C-reactive protein (CRP) measurements in 176 patients hospitalized with suspected systemic meningococcal disease (MCd) are presented. 115 patients had meningococcal disease and 61 patients had other diseases and served as control patients. On admission to hospital high CRP levels were found in patients with meningococcal disease, markedly above the levels found in patients with viral infections. The CRP level fell to nearly normal level during the first week of treatment. CRP on admission to hospital had no prognostic value. Pretreatment CRP level can be valuable in the differential diagnosis between meningococcal disease and other diseases.