The status of the central nervous system as an immunologic organ synthesizing IgG in several neurological diseases has been established convincingly in the past two decades. The measurement of intra-BBB IgG synthesis has been accomplished. It has been demonstrated that this synthesis is a potential marker for an abnormal immunologic process within the CNS which if manipulated may be a quantifiable aspect of disease modulation. Modulation of intra-BBB IgG synthesis is feasible, but there is no evidence yet that modulation of this synthesis is an index of effective disease control in MS. Only ACTH and corticosteroids lead to a significant and lasting depression of intra-BBB IgG synthesis, even though clonal eradication is not achieved. Based on our immunopharmacologic studies in MS we have proposed an immunokinetic model. The qualitative analysis of the specificity of IgG synthesized intra-BBB in MS has not led to the etiology of MS, but utilization of quantitative methods may. Questions raised by this review with suggested experiments to advance further our understanding of intra-BBB IgG synthesis as it relates to the etiopathogenesis of MS are included.