The sliding motion of organelles in a perfused characean internodal cell has been investigated. A small number of myosin molecules attached to the organelle are known to slide along actin bundles lying on the inner surface of the cell. The stepping motion of the organelles was first observed using a high-speed camera with a time resolution of 1 ms. The spatial frequency of all pairwise differences in displacement of the stepping motion has been estimated to be 0.012-0.014 nm(-1), which implies that the organelle moves with large steps of 71-83 nm along the actin bundles in a perfused characean cell.