The objective of this work was to determine if Escherichia coli methionine bioassay characteristics were influenced by selective media amended with antibiotics and the antifungal compound cycloheximide. Bacterial cells were grown in minimal media with increasing concentrations of methionine and were incubated at 37 degrees C with vigorous agitation for 6 hours. Addition of antistatic agents to the media did not change the growth kinetic response (P>0.05) to methionine concentration (3.4 to 26.8 microM). This supports the utility of this strain as a methionine bioassay organism for feed and other environmental sources.