Meningoencephalitis was recorded in 10 two- to 14-day-old calves during a two-year field study. Analysis of lumbosacral cerebrospinal fluid revealed a marked increase in protein concentration with a pronounced neutrophilic pleocytosis. Three calves with positive bacteriological cultures which were treated with chloramphenicol survived whereas six calves treated with penicillin G had to be destroyed on humane grounds after their condition deteriorated. Only two of the 10 calves had concurrent lesions of omphalophlebitis which may indicate that this is not the major route of bacterial invasion in neonatal meningoencephalitis. None of the constituents of cerebrospinal fluid proved to be a reliable prognostic indicator of meningoencephalitis. It is concluded that the analysis of cerebrospinal fluid is a useful ancillary aid in the investigation of abnormal mental states in neonatal calves and a sensitive test for the presence of an inflammatory lesion involving the leptomeninges.