In order to analyse the paper strip electrophoresis contribution to the knowledge of cerebrospinal fluid (CSF) proteins in cysticercosis of the central nervous system (CNS) 40 patients were studied (identification data in table 1); the clinical forms and diagnostic data of 30 of them, who had CNS cysticercosis (cases 1 to 30) are summarized in the table 2; cysticercosis of the CNS might play a role in the pathologic condition presented by the remaining 10 patients. CSF protein fractions were examined in all the cases (results in tables 4 and 7) and those of blood sera in cases from 1 to 15 (results in table 5) by paper strip electrophoresis under the specifications previously reported54. A second examination of CSF protein fractions was made some time later in 4 cases (results in table 6). CSF samples were analysed also in respect to cytology, total protein content, Pandy and colloidal benzoin reactions and complement fixation tests for syphillis and cysticercosis (results in table 3). The values obtained for CSF protein fractions were compared to norma) values found in 30 control subjects; these normal values were detailed in a prior publication55 and are summarized in table 8. This comparison shows that CNS cysticercosis produces changes in the electrophoretic prophiJe of CSF proteins (table 9); an increased y-globulin fraction was the main change observed, commonly associated to a low j8-globulin relative concentration. An inversion of a1/a2 quocient was found in 4 cases. The contributions to the study of CNS cysticercosis resulting from the electrophoretic analysis of CSF proteins are discussed in three groups: 1 - Informations obtained by paper electrophoresis of CSF proteins are independent from those resulting from the other laboratory aspects studied. Thus, if the protein fractions of blood sera are considered, although the changes found have mean values similar to those found to the CSF protein fractions (table 10), it was observed that there are individual differences in the protein fraction relative concentrations in blood and CSF (table 11), no correlation being found between them. Considering CSF itself, changes in its protein fractions induced by CNS cysticercosis are similar in ventricular and subarachnoid samples (lumbal and cisternal) (table 13); their intensity is related to the intensity of the whole of CSF changes (table 12). Informations obtained by electrophoretic analysis of CSF proteins, however, differ from those resulting from the other examinations conducted in the CSF sample as was shown in the analysis of cytology (tables 14 and 15), total protein content (table 16), colloidal benzoin reaction and positivity of complement fixation test for cysticercosis. 2 - The clinical value of data achieved by CSF proteins electrophoresis is discussed. Results may have an important role in diagnosis, in the knowledge of its clinical forms (table 17) and in the control of evolution if pathogenetic mechanisms involved in disease are considered. Cases 31 to 40 illustrate the clinical aspects of contributions given by CSF electrophoresis. 3 - The CSF protein fractions changes found in CNS cysticercosis justify their classification among those changes commonly observed in subchronic and chronic inflammatory diseases of the CNS and/or its leptomeningeal coverings. It is assumed in the literature that there occurs a local production of globulins, specially the y-globulin fraction, in such pathologic conditions. Concerning CNS cysticercosis, if CSF total protein content and electrophoretic data on its fractions are considered together (table IS and 19; graph. 1), it is possible to evidence that at least two mechanisms participate in the origin of protein changes (tables 20 and 21; graph. 2) : blood-CSF barrier disturbances are able to explain data concerning albumin, a and globulin changes, which are similar; the local production of y-globulin is the hypothesis most reliable to explain the peculiar changes of this fraction. This hypothesis agrees with literature data concerning other chronie inflammatory diseases of the CNS. The probable role of y-globulin in carrying specific antibodies is pointed out through correlative exploration of its concentration in the CSF sample and the corresponding positivity of complement fixation test for cysticercosis.