Amyotrophic lateral sclerosis (ALS) is a progressive neurological disease characterized by upper and lower motoneurone degeneration. Excitotoxicity and oxidative stress have been proposed as possible aetiological factors. We measured the neuronal death induced in rat cortical cell cultures by CSF taken from seven ALS patient and seven control subjects with lumbar radiculopathies. Cultures were exposed to CSF for 48 h at a dilution of 1:4. Some cultures were also exposed to antioxidant drugs, the free radical scavenger vitamin E (250 microM) and the xanthine oxidase inhibitor allopurinol (50 microM), alone or combined. The mean neuronal death rate was 31.8 +/- 3.4% in cultures exposed to ALS CSF and 10.9 +/- 1.8% in cultures exposed to control CSF. The cytotoxicity of ALS CSF was partially blocked by vitamin E (21.6 +/- 3%) or by allopurinol (18.6 +/- 2.7%). The combination of these two antioxidants reduced the toxicity from 31.8 +/- 3.4% to 10.6 +/- 1.7%. The present work suggests that neurotoxicity induced by CSF from patients with ALS indirectly involves free radicals. A combination of allopurinol and vitamin E may be useful in ALS therapy.