Methods used to analyze S-phase entry in vestibular sensory epithelia. Utricles were dissected from 2-d-old rats and incubated with the enzyme thermolysin to separate the sensory epithelium from the underlying connective tissue. The nonsensory epithelium (light gray) was trimmed away, and the remaining pure sensory epithelium was cut into four equal pieces. Pieces of epithelium were transferred to a glass-bottom culture dish in a medium containing BrdU and either vehicle or one of the test compounds. After 72 hr, the cultures were fixed and processed for immunocytochemistry and DAPI staining; next, the fraction of the cells that had entered S-phase and incorporated BrdU during replication of their DNA was calculated from counts of all of the labeled and unlabeled cells.