Both glucosinolates and S-methyl cysteine sulphoxide (SMCO) have been implicated in the suboptimal intakes observed among lambs consuming forage brassicas. However, the effects on animal performance of the compounds administered in isolation have been marginal (Barry et al, 1982) and the toxicity of the compounds may be enhanced by interactions between their physiological effects. In order to test this, an experiment was conducted in which rumen metabolites of both SMCO and the predominant kale glucosinolate, sinigrin, were administered in combination to sheep and effects on voluntary intake and blood chemistry were examined. SMCO is hydrolysed in the rumen to dimethyl disulphide by a bacterial enzyme while sinigrin undergoes hydrolysis in crushed plant tissue to allyl isothiocyanate and allyl cyanide under plant enzyme catalysis.