Plain carbon steels are primarily composed of iron (~97%), but generally have small quantities of carbon, manganese, sulfur, phosphorous and silicon also present. Lead or copper may also be present. The steel industry is in need of an on-line technique of analysis for manganese in these steels. The manganese concentration of these steels varies from 0.3 to 1.5%. A technique is presented for the rapid analysis of manganese in carbon steels using energy dispersive x-ray fluorescence spectroscopy. It is capable of determining the manganese content of a carbon steel in. less than 30 sec with an uncertainty of less than 0.05% manganese. Because this method can analyze a steel from a distance of two feet, it should be possible to adequately protect the x-ray fluorescence spectrometer from the environment even when analyses are made of hot steel ingots at temperatures ranging up to 2400°F.