Abstract The IgG index, IgM and IgA contents in cerebrospinal fluid and serum were examined retrospectively using an enzyme-linked immunosorbent assay (ELISA) in 69 dogs with inflammatory central nervous system (CNS) diseases of various aetiologies. Fifteen normal dogs were used as controls. After measuring IgG and albumin contents in serum and cerebrospinal fluid (CSF), the IgG index was calculated according to the formula of Link and Tibbling to demonstrate intrathecal immunoglobulin synthesis. A surprisingly high number of animals with encephalitis, including dogs with protracted diseases such as chronic distemper encephalitis and granulomatous meningoencephalomyelitis, showed in addition to an elevated IgG production evidence of intrathecal IgM and IgA production. The highest values of intrathecal as well as systemic IgA levels were found in dogs suffering from steroid responsive meningitis-arteritis. It was concluded that the control of the humoral immune response in the brain differs from that in other tissues. Because of striking similarities between dogs and humans in respect to humoral neuroimmunological reactions, the dog can be considered to be a useful animal model for the study of the intrathecal humoral immune response.