Limited information is available on the role of free radicals in the central nervous sy stem (CNS) and brain. Recent studies suggest, however, that free radicals are responsible for pathological c hanges in the blood-brain barrier (BBB) function. It was found that these changes resulted in disorders of BBB permeability with all possible consequences. Free radicals, being mostly very small particles, can theoretically penetrate into cereb- rospinal fluid (CSF). The aim of our paper was to estimate the concentration of free radicals in blood and CSF, in patients suffering from neurological diseases, associated with elevated BBB perm eability. As the marker of changed permeability of BBB serves, as usually, s.c. albumin-index, expressed as the ratio of serum-albumin concentration/CSF-concentration of albumin. The group of probands was divided into controls (K) (N = 20) and the group of patients (P) (N = 29). Albumin was measured by the nephelometric method using the Dade Boehring apparatus BM 2. Free radicals were estimated by an original new spectrophotometric method. For statistical evaluation of obtained values the Student’s t-test was used followed by the regression correlation analysis. Unexpected results were obtained by quantification. The free radical value in serum of probands from the control group was 2.74 ± 0.02 mg Fe 2+ , which corresponds the physiological concentration of FR in the healthy persons. No free radicals were found in CSF. In serum of patients from group P the free radical concentration was significantly elevated: p < 0.01, FR = 4.23 ± 1.45 mg Fe 2+ , but in CSF no free radicals were detected. It is not easy to explain this surprising result. We have only one logical explanation based on the hypothesis, that the organism, protecting the brain and CNS makes an effort to eliminate free radica ls by the mobilisation of those antioxidants able to penetrate the functioned BBB. It is also possible that it uses for the FR elimination the elevated albumin concentration in CSF if is damaged the BBB. The verification of this hypothesis will be our next goal.

        Key words: cerebrospinal fluid, serum, free radicals, blood-brain barrier, albumin, antioxidants.