Mice received 800 mg/kg of kanamycin base twice daily for 14 days. Solid bars: baseline ABR thresholds before drug administration; open bars: thresholds 3 weeks after the end of kanamycin treatment. N indicates the C57BL/6N substrain; J indicates C57BL/6J. Number of animals: n = 5 for C57BL/6N and n = 6 for C57BL/6J. Data are means + s.d. Significance of treatment effects within each strain (by two-way ANOVA with Sidak’s post-hoc test for multiple comparisons): N strain, F = 10.64, *0.001 < P < 0.01; J strain, F = 64.48, **P < 0.001. In contrast, there was no significant difference in the post-treatment thresholds between N and J substrains.