A laboratory method is presented for studying zooplankton swimming behaviors such as phototaxis and photokinesis . The method attempts to standardize laboratory conditions and to minimize the effects of several phenomena which modify zooplankton behavior . The role of angular light distribution in zooplankton behavior is discussed, and an apparatus which simulates a natural underwater light environment is described . The procedure minimizes the fluctuations in zooplankton swimming speed and vertical distribution that are caused by large light stimuli, noise, food deprivation, endogenous rhythms, and other factors . The experimental animals were viewed remotely with the aid of a light amplifier and video camera . A mathematical equation and computer program for calculating three-dimensional swimming speeds of zooplankton from video recordings are described in detail .