The ankle joints of 14 healthy volunteers and 16 patients with unstable ankle joints were tested for their functional and proprioceptive capabilities. All of them were active athletes. Three tests were used: the single-leg stance test, the single-leg jumping course test, and the angle-reproduction test. The influence of three stabilization devices--the lace-on brace (Mikros), the stirrup brace (Aircast), and taping--on the proprioceptivity of stable and unstable ankle joints was evaluated. The scores of the single-leg jumping course test without any stabilizing device ("standard" category) ranged between 8.06 and 13.68 (10.65 + 1.29). In the Mikros (9.95 + 0.99) and Aircast (9.99 + 1.14) brace categories, as well as the tape bandage (10.27 + 0.81) category, better scores were achieved. The differences between "standard vs Mikros" and "standard vs Aircast" revealed a significant reduction of the scores with the orthoses (P < .01). The error rate in the single-leg stance test was within the range of 0 to 16 (5.12 + 2.85) for the standard category. It was lower for the Mikros (3.65 + 2.65) and Aircast (4.17 + 2.59) categories. The error rate was highest in the tape bandage group (5.79 + 3.53). There was a significant difference between "standard vs Mikros" and "standard vs Aircast" regarding injured and non-injured ankle joints (P < .01). The angle-reproduction test showed higher values for the standard (2.36 degrees + 0.97) category than the Mikros (1.46 degrees + 0.72), Aircast (1.62 degrees + 0.91), and taping (1.84 degrees + 0.41) categories. In the standard category, the reproduction error was lower when non-injured ankle joints (2.30 degrees + 1.04) were tested than when unstable ankle joints (2.44 degrees + 0.81) were tested, whereas in all other categories the reproduction error was higher in the group of non-injured joints. According to the literature, applying a prophylactic brace can prevent an estimated 30 ankle sprains per 1000 athletic exposures.