Flubendazole and topotecan arrest, but do not eliminate, hair cell regeneration. Fish were treated with neomycin, exposed to flubendazole or topotecan for 24 hrs (or mock-treated with DMSO; cross-hatched area on abcissa), and then placed in fresh embryo media for an additional 72 hrs. A. Hair cell numbers in fish treated with flubendazole remain low while flubendazole is present (through 24 hrs). When flubendazole was removed, hair cell regeneration resumes, and by 96 hrs, hair cell numbers in flubendazole-treated and DMSO-treated controls are not significantly different. B. Similar suppression of hair cell regeneration is seen in fish treated with topotecan for 24 hrs. However, when the inhibitor drug was removed, hair cell regeneration was greatly attenuated. Hair cells were counted in 7 neuromasts per fish (n = 10 fish per group). Error bars indicate +/− 1 SD.