The study of six patients with acute intermittent porphyria is reported. Clinical and biochemical studies have been performed during the long hospitalization of the patients. The main disautonomic aspects were the arterial hypertension and the tachycardia in four patients, cardiac arrest in three patients and respiratory arrest in five patients. The cause of this problems is probably the involvment of the autonomic adrenergic system. The authors observed also three patients with hyponatremia probably resulting from inappropriate secretion of antidiuretic hormone. The prognosis of the acute intermittent porphyria is worse if the patients have disautonomic symptoms; three patients died and two had neurological sequalae (motor tetraparesis).