The article reviews literature data dealing with secondary metabolic disorders of heme precursors and their clinical significance in the context of differential diagnosis with « genuine » hereditary porphyrias. Secondary disorders of porphyrin metabolism are an insufficiently studied problem. As has been acknowledged, accumulation of copro- and uroporphirins itself cannot cause neurological symptoms similar to such in acute hepatic porphyrias. Nevertheless, the bulk of literature contains descriptions of patients with acute-onset polyneuropathies or encephalopathies, in whom coproporphyrinuria was found. The authors put emphasis on the importance of ruling out acute porphyrias in patients with combinations of polyneuropathy and abdominal pain syndrome, photosensitivity, autonomic dysfunction. Also, the article presents four authentic clinical observations of paediatric and adolescent patients, in whom acute porphyria was suspected on the basis of the clinical picture. Examination, however, revealed only a moderate increase of excretion of late heme precursors. Therefore, the diagnosis of acute hepatic porphyria was not confirmed. On the other hand, the genesis of secondary porphyrinuria in such patients, as well as the causative relations between neurological symptoms and disorders of porphyrin metabolism remain unclear.