Nebraska inmate Michael A. Mitchell appeals the district court’s dismissal with prejudice of his 42 U.S.C. § 1983 complaint, wherein he claimed Eighth Amendment violations based on his alleged exposure to environmental tobacco smoke (ETS). We affirm based on Mitchell’s failure to establish administrative exhaustion—an issue raised by defendants, but not addressed by the district court—and we therefore modify the dismissal to be without prejudice. Cf. McAlphin v. Morgan, 216 F.3d 680, 682 (8th Cir. 2000) (per curiam) (complaint properly dismissed without prejudice where plaintiff prisoner “did not satisfy his burden of showing” exhaustion).

Dismissal is required when an inmate has not exhausted administrative remedies before filing his lawsuit. See 42 U.S.C. § 1997e(a); Johnson v. Jones, 340 F.3d 624, 627 (8th Cir. 2003). Mitchell submitted no evidence of exhaustion with his complaint, and he admittedly had received no response to his most recent ETS-related grievance before he filed the instant lawsuit. We decline to entertain Mitchell’s arguments about the district court’s denial of attorneys’ fees and costs, and we deny as moot appellees’ motion for summary affirmance.