A register of the Guillain-Barrè syndrome (GBS) has been started in Lombardy on February 1 1994, aiming at: 1) Making more correct estimates of the incidence and time and geographic trends of the disease; 2) Having a target population which serves for reference for analytical and experimental epidemiological studies; 3) Contributing to the validation of selected diagnostic procedures; 4) Implementing an audit of the diagnosis and treatment of GBS; 5) Collecting biochemical, hemathological and electrophysiological data to be stored in ad-hoc data-banks. In a pilot study undertaken during the period February 1 1994-May 31 1995 a total of 109 patients (M 63; F 46) were recruited in 32 hospitals. The crude annual incidence rate of GBS was 0.92 per 100,000 population. Typical GBS had been diagnosed in 87% of cases, followed by atypical GBS (7%). The disease could not be classified according to the available criteria in 6% of cases. Electrophysiological features suggesting demyelination were present in 29% of cases; axonopathy was documented in 14%, and mixed patterns in 34%. Plasma exchange was the suggested treatment in 51% of cases, followed by immunoglobulins (24%) and steroids (23%).