Using a sensitive and specific radioimmunoassay levels of leukotriene (LT)C4-like material were estimated in lumbar cerebrospinal fluid (CSF) samples from patients with multiple sclerosis (MS) in comparison to control patients with or without inflammatory processes in the central nervous system (CNS). Levels of LTC4-like material were significantly elevated (p less than 0.01) in CSF from patients with inflammatory diseases such as meningitis, polyradiculitis or meningoencephalitis (57 +/- 53 pg/ml, n = 16) as compared to those from control patients without inflammatory or immunological CNS diseases (21 +/- 16 pg/ml, n = 42). By contrast, LTC4-like material was 16 +/- 7 pg/ml in first manifestations of MS (n = 7). 21 +/- 16 pg/ml in remitting-relapsing MS (n = 15) and 10 +/- 6 pg/ml in chronic progressive MS (n = 8). These results argue against a significant pathophysiological role of cysteinyl-LT in MS.