A study of the clinical, electrophysiological and biochemical features of 16 patients with legionellosis has been performed. Evidence of central and peripheral nervous system involvement has been found in the majority of patients. This is characterised by confusion out of keeping with the degree of toxic or metabolic upset, signs of anterior midline cerebellar dysfunction, grossly elevated creatinine kinase of skeletal muscle origin, and a subclinical peripheral neuropathy.