Grain refinement of aluminium by TiC nuclei was postulated as far back as 1950 by Cibula. This so called carbide' theory suggests that the nominal addition of Al-Ti master alloy promotes spontaneous formation of TiC by reaction with the residual carbon in the melt. The TiC so formed is virtually insoluble in molten aluminium and on cooling acts as a heterogeneous nucleation site. The observed fading behavior of the nucleants is merely a result of particle settling and/or agglomeration. In the present work synthetic TiC particles ([approximately]5--10[mu]m) have been added directly into molten aluminium by a specially developed injection technique, the details of which are presented elsewhere. Up to 2 volume percent of TiC could be added successfully while preventing oxidation of the particles during the addition process. After briefly reporting the results obtained from these experiments, it will be demonstrated that, considering the thermodynamics and kinetics of the ternary Al-Ti-C system with particular reference to the formations of Al[sub 4]C[sub 3] and Ti[sub x]AlC compounds on TiC, the carbide' theory is highly suspect.