AbstractCytoplasmic dyneins play a role in a myriad of cellular processes, such as retrograde intracellular transport and cell division. Small-molecule cytoplasmic dynein antagonists, ciliobrevins, have recently been developed as tools to acutely probe cytoplasmic dynein function. Although widely used to investigate cytoplasmic dynein 1, far fewer studies explore the effect of ciliobrevin on cytoplasmic dynein 2 or IFT dynein. Here, we use ciliobrevin A to partially disrupt IFT dynein in the chemosensory cilia of living C. elegans. Acute, low-concentration ciliobrevin treatment results in shortening of cilia and reduction of transport velocity in both directions. After longer exposure to ciliobrevin, we find concentration-dependent motor accumulations and axonemal deformations. We propose that maintenance of ciliary length requires a high fraction of active IFT-dynein motors, while structural integrity can be preserved by only a few active motors.