Chemotactic behavior as a function of growth stage in an Escherichia coli strain commonly used for chemotaxis studies was characterized using computerized image analysis. The response and adaptation to saturating, step-like additions of the attractant L-aspartate were measured. Steady-state average tumbling frequency and adaptation time increased nearly twofold during logarithmic phase. In contrast, precision of adaptation, P, defined as the ratio between steady-state tumbling frequencies in the presence and absence of attractant, appeared to be constant throughout growth (P = 1.0 +/- 0.2). The variation of tumble duration over growth was consistent with a hydrodynamic mechanism for tumble termination.