The author reports the results of quantitative and qualitative investigations of immunoglobulins in the cerebrospinal fluid in multiple sclerosis and their evaluation in the aspect of their diagnostic usefulness. Determinations of the relative Ig level and the IgG index were of greater diagnostic usefulness than determinations of absolute Ig level. Already determination of the absolute level was valuable in cases with normal total protein level in the fluid. The results of quantitative determinations of Ig in the fluid were insufficient, however, for differential diagnosis against the group of diseases with local Ig production. Evaluation of the oligoclonal character of Ig in the fluid based on electrophoretic separation in agar and agarose was very useful in the diagnosis, but this phenomenon occurs also in a limited group of other central nervous system diseases. The abnormal ratio of kappa to lambda chains in the cerebrospinal fluid is of decisive importance for the diagnosis of multiple sclerosis. Complex quantitative and qualitative determinations of Ig in the cerebrospinal fluid are a significant advance in the diagnosis of multiple sclerosis making possible the correct diagnosis in cases with monosymptomatic or oligosymptomatic onset already in the first stage of the disease, and also in clinically silent periods e.g. before the first phase of the disease.