This study examined whether the provision of norepinephrine, as would be encountered within the highly innervated gastrointestinal system, affected the growth rate of enterotoxigenic Escherichia coli (ETEC) and the expression of the K99 pilus adhesin virulence-related factor. The addition of norepinephrine to serum-containing medium resulted in a 3- to 7-fold increase in the growth rate of the K99+ ETEC strain B44 as compared to growth in vehicle supplemented medium or medium supplemented with normetanephrine, a norepinephrine metabolite that contains one more methyl group than norepinephrine. ELISA analysis revealed that K99 pilus adhesin expression was increased in norepinephrine supplemented culture as compared to normetanephrine and vehicle supplemented controls. This increase occurred from 9 to 15 hours of incubation which represented the exponential growth phase for the norepinephrine supplemented culture. These results indicate that addition of norepinephrine affects both ETEC growth and expression of a specific virulence factor.