The electrostatic interaction between two capacitively coupled, series-connected metal double dots is studied at low temperatures. Experiment shows that when the Coulomb blockade is lifted, by applying appropriate gate biases, in both double dots simultaneously, the conductance through each double dot becomes significantly lower than when only one double dot is conducting a current. The conductance lowering seen in interacting double dots is compared to that caused by an external ac modulation applied to the double-dot gates. The results suggest that the conductance lowering in each double dot is caused by a single-electron tunneling in the other double dot. Here, each double dot responds to the instantaneous, rather than average, potentials on the other double dot. This leads to correlated electron motion within the system, where the position of single electron in one double dot controls the tunneling rate through the other double dot. ©1998 American Institute of Physics.