Diagnosis of porphyria is a clinical and biochemical procedure. Acute hepatic porphyrias are molecular regulation diseases which are characterized by a relative enzyme deficiency of the ferro-chelatase chain and an induction of hepatic delta-aminoacid synthase. There are indistinct clinical and pathobiochemical transitions between the three acute hepatic types of porphyria: acute intermittent porphyria, hereditary coproporphyria and porphyria variegata. They develop a similar acute clinical syndrome. The differential diagnosis is made possible by a differentiation of porphyrins and porphyrin precursers in the urine and the porphyrines in the stool and by the determination of uroporphyrinogen synthase activity in the erythrocytes.