The cybernetic framework is a mathematical formalism developed by Ramkrishna and coworkers for modelling microbial systems. In this work, we analyze the dynamics of the cybernetic model for diauxic growth (Kompala et al., 1986, Biotechnol. Bioengng. 28 1044-1055). Recent data shows, however, that microbial growth on binary mixtures is frequently nondiauxic. The goal of this work is to : (1) Understand why the model captures the diauxie. (2) Determine if the model can embrace the nondiauxic growth patterns. The analysis shows that the global dynamics of the cybernetic model agree with diauxic behavior, and the autocatalytic nature of enzyme synthesis plays a key role in ensuring this agreement. But there exists no set of parameter values for which the model embraces the nondiauxic growth patterns; this observation is specific to the model of Kompala er al. (1986) and does not apply to the more recent cybernetic model of Ramakrishna et al. (1997, Biotechnol. Bioengng 52, 141-151).