Steroid responsive meningitis-arteritis in 32 cases was studied. Two forms were recognised: The typical form showing cervical rigidity and pain, fever and pleocytosis with polymorphonuclear cells in the cerebrospinal fluid (CSF); and the atypical form, a more protracted type characterised by additional neurological deficits and lack of typical CSF changes. Both groups responded to steroid application. Several ancillary laboratory procedures were applied in an attempt to improve the diagnosis. Electroencephalography was found to be helpful in detecting an inflammatory process. Measuring IgA levels in the serum and CSF was also another useful technique for detecting atypical cases. Long-term treatment with prednisolone was undertaken in 20 dogs. The treatment was monitored by rigorous control examinations of the blood and CSF at regular intervals. Twelve dogs were considered cured after this treatment. Thirteen dogs were euthanased; five of these in the acute stage of the disease and eight because of progressive neurological disease. In all these cases histopathological examination was performed. The data are compared to reports in the literature on meningitis and arteritis in dogs and the pathogenesis of the disease is briefly discussed.