The expression levels of initiating components of the classical pathway (C1qB and C4), the alternative pathway (factor B), the lectin pathway (mannose binding lectin 1 and 2), the central component common to all pathways, C3, and the complement regulators CD55 and CD59a were measured in the lumbar spinal cord of hSOD1G93A mice during disease progression of ALS (30 to 175 days). The gene discussed is C3; the disease is amyotrophic lateral sclerosis.