The characteristic symptoms for acute porphyrias are caused by the inherited decreased activity of the enzymes of the heme biosynthesis pathway. Usually there is an exogenous or endogenous factor inhibiting the heme biosynthesis or increasing the consumption of heme produced in already decreased amount. The most important precipitating factors are the therapeutic drugs. Therefore, certain therapeutic drugs ordered for carriers or patients with acute porphyria are serious risk factors. It is very important to identify patients and carriers with acute porphyria as early as possible and to make a close follow-up so the development of the symptoms of the life threatening acute attack could be prevented. It is very difficult to suspect the diagnosis of acute porphyria. There is a very characteristic discrepancy between the serious complaints and the actual clinical findings. The severe cramping abdominal pain, nausea, vomiting, muscle weakness of the limbs and sensory loss are the main signs at the beginning. The specific symptoms which help to establish the diagnosis--red-colored urine, hyponatremia, tachycardia, hypertension, subileus, acute psychosis, gradually developing paresis of the lower and then the upper limbs--are characteristic for the later phase of the acute attack. Very often there is a rapid progression with Landry-type paralysis developing in days or even in hours, following respiratory paralysis or serious arrhythmia is the cause of the death. In case of suspicion of acute porphyria the patient should be directed to a department where the specific laboratory methods--measurement of the porphyrin precursors, porphyrins and their isomers in urine and feces, quantitation of protoporphyrin in red blood cells, measurement of the plasma porphyrin and enzyme activity--to diagnose the different types of the disease and the immediate specific treatment with heme arginate are possible if needed. All of these are available in the National Porphyria Center.