The analyses of porphyrins and their precursors in urine, blood and feces are essential for establishing the diagnosis of hereditary porphyrias and for screening for occupational or industrial disease caused by exposure to lead dust or fumes. While porphyrins can easily be separated and extracted by the solvent-extraction method or various chromatographic procedures and provide information of diagnostic importance, high-performance liquid chromatography can now be best used for the separation and determination of porphyrins for differential diagnostic purposes. Where there is need for making a definite diagnosis, determination of activities of enzymes involved in the heme biosynthesis in erythrocyte or lymphocyte and/or genetic diagnosis would be the most reliable way of addressing the problem. These diagnostic techniques, however, are based on highly specialized scientific knowledge and discipline and not suitable for general use. In this paper, a description is given of the most widely used biologic diagnostic criteria and the diagnostic technique underlying them in current use.