(A) Effect of 50% atmosphere of the inert gases xenon (red bars), argon (cyan bars), krypton (brown bars), and neon (green bars) on control traumatic injury (black bars) at 24, 48, and 72 h after injury. Sham-treated slices (white bars) were not subject to trauma. Xenon and argon provided significant neuroprotection at all time points. Xenon was more effective than argon, with xenon-treated slices being 57 ± 1% of control injury compared with 70 ± 6% of control injury for argon-treated slices, 72 h after injury. None of the other inert gases provided significant protection against injury at any of the time points. The error bars are standard errors. The data have been normalized to the control injury at 72 h after injury. *Indicates value significantly different (P < 0.001) from control injury at each time point. #Indicates value significantly different (P < 0.01) from control injury (N = 141 control traumatic injury; N = 105 sham; N = 104 xenon; N = 44 argon; N = 45 krypton; N = 22 neon). (B) Concentration–response relationship for neuroprotection by xenon and argon. Xenon (filled circles) exhibited a neuroprotective effect at a concentration of 30% atm, with 40 ± 8% protection, increasing to 52 ± 13% protection at 70% atm xenon. In contrast, argon (open circles) was not neuroprotective at 30% atm but did exhibit a protective effect at concentrations of 50% atm and 70% atm argon. Lines shown were drawn by eye and have no theoretical significance. Error bars are standard errors (50% xenon: N = 104; 30% xenon: N = 6; 70% xenon: N = 6; 50% argon: N = 44; 30% argon: N = 14; 70% argon: N = 10).