We report an episode of aseptic meningitis in a 53-year-old man, who was treated with infliximab for active rheumatoid arthritis. He had acute, severe muscle pain after initial infusion of the drug, and similar symptoms with a transient lymphocytic meningitis after a subsequent infusion. We measured no change in antibodies to nuclei, DNA, or to neurones. Functional antibodies to infliximab were not induced and concentrations of tumour necrosis factor a in spinal fluid were not raised. This adverse reaction to infliximab might have been caused by inability of the drug to enter the central nervous system.