Steel which is subjected to a tensile stress exceeding some critical value depending on the strength level of the steel and which contains hydrogen that is free to move is susceptible to failure in a delayed, brittle manner. The problem is especially serious because the minimum stress for failure decreases as the strength of the steel is increased and because failures occur with no appreciable ductility, even though in a tensile test the material may exhibit normal ductility. Under most conditions the strength level of the steel is the most important factor affecting the occurrence of delayed, brittle failure. Both the minimum applied stress that will result in failure and the time required for the failure to occur decrease as the tensile strength of the steel is increased. These failures occur in all types of steel microstructures except austenite. Alloy composition is a relatively unimportant factor in the hydrogen-induced, delayed, brittle failure of body-centered cubic steels.