-Introduction: Multiple sclerosis (Ms) is a chronic, inflammatory and progressive disease of the central nervous system in which local inflammatory injuries of the brain white matter appears, being the most outstanding feature the myeline loss (demyelination). Objective: to determine if the complement system might be involved in the Ms immunopathogeny favouring the mechanism intervening in the myelin destruction. Method: samples of sera and csF from twelve patients with a diagnosis of Ms obtained at the moment of the admission to the hospital at the beginning of the break out, were collected. Levels of c3c and albumin in sera and in csF were quantified using radial immunodiffusion plates. Results: High values over 80% of intrathecal synthesis were obtained except in one of the patients. Conclusion: Intrathecal synthesis of c3c and its liberation to the csF means that the activation of the complement system in any of the two ways has taken place, and that once performed its biological functions, has suffered a degradation process Key words: cytotoxicity, complement, multiple sclerosis, hypersensibility, immunopathogenicity, reibergram.evaluaci贸n de la s铆ntesis intratecal de C3c en pacientes con esclerosis m煤ltiple resuMeN -Introducci贸n: La esclerosis m煤ltiple (eM) es una enfermedad cr贸nica, inflamatoria y progresiva del sistema nervioso central que cursa con la aparici贸n de lesiones inflamatorias focales en la sustancia blanca cerebral, en las que lo m谩s llamativo es la p茅rdida de mielina (desmielinizaci贸n). Objetivo: conocer si el sistema de complemento puede estar involucrado en la inmunopatogenia de la eM favoreciendo los mecanismos que median la destrucci贸n de la mielina. M茅todo: se colectaron muestras de suero y Lcr de doce pacientes con diagn贸stico de eM obtenidas en el momento del ingreso al inicio del brote. se cuantificaron los niveles de c3c y alb煤mina en suero y en Lcr en placas de inmunodifusi贸n radial. Resultados: se obtuvieron altos valores que superan el 80% de s铆ntesis intratecal, menos en uno de los pacientes. Conclusion: La s铆ntesis intratecal de c3c y su liberaci贸n al Lcr significa que ha sucedido la activaci贸n del sistema de complemento en alguna de las dos v铆as y que una vez cumplidas sus funciones biol贸gicas, ha sufrido un proceso de degradaci贸n y liberaci贸n al Lcr en forma de c3c.PALABrAs-cLAve: citotoxicidad, complemento, esclerosis m煤ltiple, hipersensibilidad, inmunopatogenia, reibergrama.