Byrne, DJ, Browne, DT, Byrne, PJ, and Richardson, N. Interday reliability of the reactive strength index and optimal drop height. J Strength Cond Res 31(3): 721–726, 2017—The purpose of this study was to investigate the interday reliability of the reactive strength index (RSI) and optimal drop height (ODH) identification from multiple drop heights. Nineteen male trained hurling players (23.1 ± 2.9 years, 83.1 ± 15.5 kg, and 182.5 ± 4.89 cm) completed 2 maximal depth jumps from 4 incremental drop heights (30, 40, 50, and 60 cm), over 2 separate testing sessions 48 hours apart. The RSI and ODH were analyzed for reliability using intraclass correlation coefficient (ICC) and coefficient of variation (CV). The RSI and ODH both demonstrated good reliability with ICC ≥0.80 (0.87 and 0.81) and CV ≤10% (4.2 and 2.98), respectively. The results of this study support the use of an incremental depth jump protocol to find the RSI and ODH in trained hurlers. It is recommended that the incremental depth jump protocol be used when assessing an athlete's reactive strength, as it allows a reactive strength profile, maximum RSI, and an ODH to be determined, all of which can provide vital information when determining an athletes training intensity and load.