Inter-organisational systems (IOS) form the backbone of today’s e-commerce between organisations. However, very little is reported about how these systems are introduced. An exception is the work of Rahim et al (2006; 2007) who proposed the IOS Adoption Motivation model (IMM). This model explains variations in IOS introduction processes by relating organisational motivations for adopting a given IOS solution. The model has been partially tested using qualitative case study protocol. As a result, the statistical generalisation of the model is not yet possible. This paper makes an attempt to evaluate an instrument which measures organisational motivations for IOS adoption and then describes a rigorous qualitative process to validate that instrument. The instrument is useful to the e-commerce researchers because it enables them to establish statistical generalisibility of IMM model. It is also beneficial to e-commerce/IT managers because it enhances their confidence in the ability to use the IMM model to avoid the uncertainty associated with IOS introduction by choosing appropriate adoption process.