Four patients with botulism were studied on admission and at different times after intoxication, using a battery of cardiovascular autonomic tests. The results were compared with clinical status and single-fiber electromyographic findings. In the early stage of intoxication, the control of heart-rate and blood-pressure responsivity was markedly impaired, as was the neuromuscular transmission. At follow-up, results of sympathetic tests normalized earlier than those of parasympathetic tests. The recovery of autonomic function was slower than that of neuromuscular transmission in three patients. Monitoring autonomic derangement in botulism adds further information on the course of the disease and may identify patients at risk for cardiac or respiratory arrest. Further clinical investigation can help in determining more precisely the autonomic sites where the toxin acts.