The motion of optically detected organelles in myelinated axons of Xenopus laevis was studied in axons bathed in a potassium glutamate based medium and in axons in a similar medium to which various inhibitors of axonal transport were added. Organelles in the potassium glutamate medium had a motion which was indistinguishable from that previously described for organelles in axons bathed in a conventional physiological saline. Colchicine, dimethylsulphoxide, 2,4-dinitrophenol, hyperosmotic solutions, raised concentrations of intracellular calcium ions, and media made up in deuterium oxide caused either a complete or partial inhibition of both anterograde and retrograde organelle transport. When directioned transport had been inhibited by any of the agents used, organelles displayed a longitudinally oriented oscillatory motion. An analysis of the variable, or oscillatory, component of organelle motion in axons not treated with inhibitors and in axons in which transport was partially or completely inhibited produced evidence that the dominant frequency components were similar in each case. A maximal estimate of the dominant frequency of oscillatory motion was 0.18 +/- 0.02 Hz. The distribution of instantaneous velocities about the mean velocity was not substantially altered as the transport of organelles was inhibited. The evidence suggested that the variable component of motion of organelles which show directioned transport is related to the oscillatory motion of organelles whose transport is inhibited.