Nominally 0.4 mm diameter high resilience stainless steel orthodontic spring wires, as used in appliances (or braces) for the correction of children's malaligned teeth, are notoriously inconsistent in their clinical behaviour. This is principally due to a lack of compositional control and to the severe work hardening of the wire drawing process. A selection of the spring wires in clinical use has been investigated here to characterise them by means of spectrochemical analysis, tensile testing, potentiostatic polarisation, and ferromagnetic measurements. The study of these interrelating factors is suggested as a method of characterisation for the wires to ensure greater clinical consistency. The effects of bending and low temperature heat treatment on the wires have also been investigated.