The authors emphasize the importance of the cerebrospinal (C. S. F.) fluid in the diagnosis of nervous system cryptococcosis. They have diagnosed 8 cases in these last three years by the C. S. F. examination and they are of the opinion that the growing reports on this disease in the litterature is due to the awareness on the part of the physician. With the acquired experience in these cases they explain how to deal with the C. S. F. in order to identify the parasite in the daily laboratory work. It is possible to suspect the presence of the fungus in the cell counting chamber where they look much alike an erythrocite. A skilled technician may tell them apart by observing the interior structure, the capsule, the budding cells, or by the acetic acid test. The stained smear for cells study shows the cryptococcus inside their gelatinous capsules, isolated or conglomme-rated. We may find honey comb looking structures, which stand for the empty spaces left by the parasites swept away during the smear confeccion. We may also observe the fungus into the giant cells. The cryptococcus is very easy to identify after the Gram and Ziehl stain. But the best way to demonstrate the fungus is by means of the India ink, where it looks very charateristic with the wide capsule and budding formation. The culture in Sabouraud medium is obtained easily in two or three days. The authors describe the C. S. F. changes in their cases. There was always hypertension. The cell count was as high as 411 and as low as 9 per cubic milimeter. In two cases there was 9 and 18 cells per cubic milimeter only, in spite of the cloudness of the fluid. This pointed out for the high number of parasites no matter how the low cell count is. The cells were mainly of the mononuclear type. The protein content was increased, between 32 and 140 mg per cent. The sugar content was low. The cryptococcus was always in great number, the highest count being 1.800 per cubic milimeter. In a subacute case the authors examined the C. S. F. at weekly intervals and observed the progressive intensification of the changes. Two chronic cases, observed over years, were mistaken for tuberculous meningitis at first. Later, a new spinal fluid test made the correct diagnosis by finding of the yeast organisms. In cryptococcosis the spinal fluid changes look very much like that of tuberculous meningitis.