AM-350 and AM-355 are controlled-transformation precipitation-hardening steels. AM-350 is more familiarly known in sheet and AM-355 in bar form where hardening is produced by heat treatments alone. Annealed at 1900 F, the materials are essentially austenitic at room temperature, but the austenite is very unstable. By cold deformation, a substantial amount of martensite is formed. The mechanical properties of cold-rolled products can be controlled over a wide range and vary as functions of per cent deformation, amount of martensite produced, and tempering treatment. The mechanical properties of these materials are extremely interesting from an engineering point of view. Higher strength with better toughness can be attained than with Type 301, which is the stainless steel generally used in the cold-rolled condition. This paper deals with the metallurgy and properties of cold-rolled AM-350 and AM-355. The mechanical properties are shown as functions of the amount of deformation, deformation temperature, and prior annealing temperature. More detailed mechanical properties of AM-350 and AM-355 CRT (20 to 30 per cent reduction) are given including toughness studies. AM-350 in particular has been evaluated for the supersonic transport and appears to meet the stringent requirements for this application.