Sterilant challenge device for use in steam sterilizers are described, including devices suitable for determining the efficacy of the non-condensable gas removal stage of a sterilization cycle and/or the quality of steam sterilant in relation to its content of non-condensable gas(es) are disclosed. Sterilant challenge devices having a metal tube having a defining a free space which is open at one end for the entry of sterilant and closed at the other end and at least one thermal load located around the tube are also described.