Porphyria is making increasing demands on the attention of clinicians and research worker. An account is given of hepatic forms, since these have recently come into prominence on account of recent advances in the understanding of their metabolic, diagnostic and therapeutic aspects. A description of the physiopathology of porphyrin metabolism is followed by an examination of the incidence, genetic features, aetiology, pathogenesis, pathological anatomy, symptomatology, diagnosis, prognosis, and treatment of each form. Particular attention is devoted to intermittent acute and cutanea tarda porphyria, since these are more commonly encountered in practice. Personal experience gathered in a large series of cases of cutanea tarda porphyria is presented.