Basic biochemical and cytological examination and evaluation of acute phase proteins, immunoglobulins, markers of compression, markers of tissue destruction, complement and proteinase inhibitors was performed on 54 samples of cerebrospinal fluid (CSF) in patients with neuroborreliosis. From the clinical point of view we differentiated 41 cases of acute infection and 13 cases of late, chronic stage (7 cases of chronic infection of CNS, 6 cases of chronic infection of PNS). The control group consisted of 464 samples of CSF from patients with normal cytological and biochemical findings. The findings in late, chronic forms compared to early, acute phases showed lower values especially in cell count, with the most common picture of monocytic oligocytosis, which is a non-specific late-inflammatory phase. In CSF proteins we observed lower mean values of inflammatory markers. Contrary to the acute ones, there is no marked elevation of the C3 compound of component in chronic forms. In a high percentage of late forms, there is elevation of IgA, and especially of its ratio, in chronic CNS infection in 100 pe cent of cases. Mos t common in chronic forms is the intrathecal synthesis of IgG. In approx. a quarter of chronic cases is possible t o find the synthesis in IgM. This fact is in consistent with the hypothesis of the possible duration of antibody production in IgM class in CSF even in the chronic phase.

        Key words: neuroborreliosis, cerebrospinal fluid.