This study analyses the innovative and imitative behavioural forces which can be found in the literature concerning diffusion of innovations. As a new element, the study extends the field of analysis to an organisational innovation such as franchising. With this we expect to cover a large gap detected in the diffusion of organisational innovation literature which, up to now, has not taken franchising into account as such. The study raises the comparison among a family of nested diffusion models, analysing previously the convenience of the imitation hypothesis underlying these models. The comparison of the models tries to analyse whether the diffusion process of the organisational innovation can be suitably represented by a model with a specific functional form. For this reason, the study proceeds estimating the model parameters and finishes with the analysis of the models' predictive ability. The results obtained from the analysed sample, support the thesis maintains by the literature concerning these behavioural forces. These forces are determining factors in explaining the modus operandi of the adopting agents. In this case, these explain the adoptive character of the Spanish firms in relation to an organisational innovation, such as franchising, during the period 1974-1999.