Contrary to the belief that porphyrias are of relatively rare occurrence, there has recently been a rapidly increasing number of reported cases of the disease apparently as a result of growing interest of clinicians, the advance of biochemical and molecular biological research works and improvement and refinement of diagnostic techniques. Unfortunately, however, it is an unquestionable fact that porphyrias are not infrequently still misdiagnosed. Detection and identification of the porphyrias constitutes an important step in the treatment of the diseases and, accordingly, determination of porphyrins and their precursors is of paramount therapeutic importance. While porphyrins are normally detected in small amounts in healthy individuals, these compounds are excreted in large quantities in the urine or feces or both in hereditary and chemical porphyrias, owing to inborn errors in heme biosynthesis and in hemolytic anemia, as a result of excessive production, resulting from increased heme biosynthesis. It follows that determination of porphyrins and their precursors in clinical materials is of pivotal importance in establishing the diagnosis of porphyrias. This paper reviews the methods of determination of porphyrins and their precursors in clinical materials and techniques employed for this purpose.