The diurnal vertical distribution and drift of zooplankton were examined in a deep (2.6 m), second order, stream pool in northcentral Arkansas. Zooplankton densities were substantial (max. > 1500/L) with the majority of the organisms occurring near or at the bottom. A significant increase in the density of copepods and rotifers occurred at 1 m during afternoon and evening hours, respectively. No increase was observed for Cladocera. Significantly more zooplankton drifted into the pool at night than drifted out. Increased densities during the night at both upstream and downstream sites were significant for all zooplankton groups except copepods at the downstream site.