T -cells are present in the spinal cord from patients with amyotrophic lateral sclerosis (ALS), and could attack neurons or activate microglia through secretion of cytokines. We report that interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-2, IL-4, IL-5 and IL-10 could not be detected in cerebrospinal fluid (CSF) samples from 15 ALS patients and 23 out of 25 controls with a multiplexed cytometric bead assay. In vivo activated T-cell clones were established from CSF (n = 26) and blood (n = 21) of one ALS patient. The proliferative capacity of CSF T-cell clones was lower than that of T-cell clones from blood (p = 0.0007). All CD4+ CSF T-cell clones produced IFN-gamma, compatible with a predominant T helper (h) 1 phenotype, but several T-cell clones also produced Th2 cytokines. These data suggest that in vivo activated intrathecal T-cells can be induced to secrete cytokines which may play a role in ALS.