The complications arising from two different anti-rabies vaccines were compared: DEV (duck embryo vaccine; the schedule included 14 daily doses plus 3 boosters) and HDCV (human diploid cells vaccine; the schedule included 5 doses plus 1 booster). 2646 patients were immunised, following a post-exposure prophylaxis, at the Antirabies Unit of the Institute of Hygiene of Rome. Among the 1434 patients immunised with DEV, 364 (25.38%) developed side-effects, whilst among the 1212 subjects immunised with HDCV only 47 (3.88%) developed side-effects. Using DEV the more frequent complications were as follows: fever (48.62%), regional adenopathy (49.45%), erythema (89.29%), local induration (41.48%). Using HDCV the main complication was fever (65.96%). The principal association of complication in DEV were: erythema + induration + edema + adenopathy + fever; general malaise + asthenia + adenopathy; dizziness + headache. Hyperthermia resulted often associated with regional adenopathy and the general malaise with the headache in the vaccinated with HDCV. All complications were widely distributed during the period of immunisation. However most side-effects arose following the 5th DEV dose or the 2nd HDCV dose. Regional adenopathy, was the more persistent and less tolerated symptom, also local erythema showed a long persistence, whilst the other symptoms regressed within 48-72 hours with proper therapy and rest. Sex and age did not influence the incidence nor the type of complications. Neither neuroparalysis was detected nor serious impairment of health. In our study the coincidence of unwanted effects, following an antirabies immunisation, seems lower than that described in the literature. This was probably due to the high level of purification of the vaccine and possibly to the different recording of the minor symptoms.