Hydroxylated fullerenes (C₆₀OH(x)) or fullerols are water-soluble carbon nanoparticles that have been explored for potential therapeutic applications. This study assesses acute in vivo tolerance in 8-wk-old female Sprague-Dawley rats to intravenous (iv) administration of 10 mg/kg of well-characterized C₆₀(OH)₃₀. Complete histopathology and clinical chemistries are assessed at 8, 24, and 48 h after dosing. Minor histopathology changes are seen, primarily in one animal. No clinically significant chemistry changes were observed after treatment. These experiments suggest that this fullerol was well tolerated after iv administration to rats.