Systemic 5-FU treatment caused delayed increases in auditory brainstem response (ABR) inter-peak latencies P2-P1 and P3-P1. Baseline ABR hearing tests were performed on each animal one day before initiation of treatment with 5-FU (as for Figure 4). After treatment ended, follow-up ABR tests were conducted on each animal at various points during a time course of 56 days. Control and treatment groups both consisted of n = 4 animals. ABR latencies were analyzed for each individual at each time point, and change of latency was calculated as Lt – L0 (Lt, latency values at day 1, day 7, day 14, or day 56 post treatment; L0, baseline latency values 1 day before treatment initiation). (a) The change of inter-peak P2-P1 latency values; (b) the change of inter-peak P3-P1 latency values. At the later time points day 14 and day 56, both P2-P1 and P3-P1 inter-peak latency values of 5-FU-treated animals show average increases of more than 0.13 ms, whereas the same inter-peak latency values of sham-treated controls show average decreases or an increase of less than 0.04 ms. Data are mean ± s.e.m. Statistical significance of the difference between the means of control and treated groups was p < 0.05 in (a), and p < 0.01 in (b) (confidence interval = 95%; paired, one-tailed Student's t-test).