The purpose of this study was to evaluate the immediate influence of eccentric muscle action on vertical jump performance in athletes performing sports with a high demand of explosive force development. In this randomized, controlled crossover trial, 13 Swiss elite athletes (national team members in ski jump, ski alpine, snowboard freestyle and alpine, ski freestyle, and gymnastics) with a mean age of 22 years (range 20-28) were randomized into 2 groups. After a semistandardized warm-up, group 1 did 5 jumps from a height of 60 cm, landing with active stabilization in 90+/-knee flexion. One minute after these modified drop jumps, they performed 3 single squat jumps (SJ) and 3 single countermovement jumps (CMJ) on a force platform. The athletes repeated the procedure after 1 hour without the modified drop jumps. In a crossover manner, group 2 did the first warm-up without and the second warm-up with the modified drop jumps. Differences of the performance (jump height and maximal power) between the different warm-ups were the main outcomes. The mean absolute power and absolute height (without drop jumps) were CMJ 54.9 W [middle dot]-1 (SD= 4.1), SJ 55.0 W [middle dot] kg-1 (SD= 5.1), CMJ 44.1 cm (SD= 4.1), and SJ 40.8 cm (SD= 4.1). A consistent tendency for improvement with added drop jumps to the warm-up routine was observed compared with warm-up without drop jumps: maximal power CMJ+ 1.02 W [middle dot] kg-1 (95% confidence interval [CI]=+ 0.03 to+ 2.38), p= 0.045; maximal power SJ+ 0.8 W [middle dot] kg-1 (95% CI=-0.34 to+ 2.02), p= 0.148; jump height CMJ+ 0.48 cm (95% CI=-0.26 to+ 1.2), p= 0.182; SJ+ 0.73 cm (95% CI=+ 0.36 to+ 1.18), p= 0.169. Athletes could add modified drop jumps to the warm-up before competitions to improve explosive force development.