ISOPROPYL-n-PHENYL carbamate (IPC), a pre-emergent herbicide1, decreases growth of roots, shoots and leaves2 and induces micronuclei. On the ultrastructural level, low concentrations of IPC in dividing Haemanthus endosperm cells disorient microtubules involved in spindle formation3. Shed-regenerating stentors, known to be producing ciliary microtubules (see ref. 4 for discussion of complete band and in situ stentor oral cilia regeneration), are reversibly sensitive to colchicine5. The mechanism of action of IPC is thought to involve inhibition or disorientation of microtubules, so, by analogy with colchicine, IPC should interfere with regenerating cilia. These experiments were designed to compare the effects of IPC on cilia regeneration, growth and macronuclear morphology with the known effects of colchicine on these parameters5,6.