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Growth hormone (GH) was upregulated in the zebrafish inner ear following sound exposure in a previous study. To identify the specific role of GH in hair cell regeneration and the possible cellular mechanisms of this regeneration, groups of zebrafish were divided into baseline (no sound exposure, no injection), buffer-injected and GH-injected groups. Buffer- and GH-injected fish were exposed to a 150 Hz tone at a source level of 179 dB re 1 μPa root mean squared (RMS) for 36 h. Phalloidin-staining was used to assess the effects of GH on hair cell bundle density; BrdU-labeling was used to assess the effects of GH on cellular proliferation; TUNEL-labeling was used to assess the effects of GH on apoptosis in the zebrafish inner ear following acoustic trauma. The time-course of hair cell bundle density, cell proliferation, and apoptosis was established by combining data for baseline fishes and sound-exposed fishes at post-sound exposure day 1 (psed1), psed2, and psed3. GH-injected fish exhibited greater densities of hair cells than bufferinjected controls. In addition, GH-injected fish had higher levels of cell proliferation and lower levels of apoptosis than buffer-injected controls. This suggests that GH may play an important role in zebrafish inner ear hair cell regeneration by stimulating cellular proliferation and inhibiting cellular apoptosis.