To describe the various conditions of peripheral nerve, neuromuscular junction, and muscle associated with the systemic inflammatory response syndrome (SIRS). Publications in the scientific literature and personal observations during the last 15 yrs. Computer search of the literature and review of patient records relating to polyneuropathy, neuromuscular transmission defects, and myopathies associated with sepsis, the septic syndrome, and SIRS. SIRS is a new concept in which infection and trauma induce a systemic inflammatory response affecting the microcirculation to organs throughout the body. The nervous system is commonly affected in the forms of septic encephalopathy and critical illness polyneuropathy. Neuromuscular blocking agents and corticosteroids may have additional toxic effects on the neuromuscular system that are manifest as transient neuromuscular blockade, an axonal motor neuropathy, or a thick filament myopathy. Clinical examination in the critical care unit is often unreliable and electrophysiologic studies, at times accompanied by magnetic resonance imaging of the spinal cord, measurement of the circulating creatine phosphokinase concentration, and muscle biopsy, are often necessary to establish the diagnosis. Variants of critical illness polyneuropathy may occur outside the critical care unit. The precise mechanism of these neuromuscular conditions is not known, and further basic research is needed. A variety of neuromuscular conditions complicates SIRS. The identification of these conditions is important in patient management and in rendering a prognosis.