Lithium chloride, more specifically the lithium cation, has been implicated in interference in biological systems. In the case of Escherichia coli, interference involves the Na+(Li+)/H+ antiporter transport system. The study reported here concerns the effects of LiCl on a mixed enrichment culture that is able to biodegrade both methanol and acetone under aerobic conditions. The results obtained using unsteady state continuous flow culture techniques demonstrate a significant disruptive effect of LiCl on culture performance. In addition, a reduction in the substrate-based biomass yield coefficient, which is a clear advantage as far as biotreatment process performance is concerned, also occurs. The ultimate fate of the LiCl was not determined.