The effects of ethanol on the brain are concentration dependent. Low concentrations (mM) intoxicate, while greater than 100 mM anaesthetize. Of most relevance to human alcohol addiction are mechanisms of intoxication. Previously, Caenorhabditis elegans has been employed in genetic screens to define effectors of intoxication. Here, we inform interpretation of these studies by providing evidence that ethanol rapidly equilibriates across C. elegans cuticle. Importantly, the effect of ethanol on muscle activity rapidly reaches steady-state, and the concentration-dependence of the effect is very similar in intact animals and exposed muscle. Thus the cuticle does not present an absorption barrier for ethanol, and furthermore the internal concentration is likely to approach that applied externally. Thus, modelling intoxication in C. elegans requires exposure to external ethanol less than 100 mM. Furthermore, the permeability of the cuticle to ethanol enables analysis of precisely controlled concentration-dependent effects of acute, chronic, and episodic ethanol exposure on behaviour.