The clinical use of dantrolene has been associated with hepatotoxicity, thus the toxicity of dantrolene in Swiss-Webster mice was characterized. Animals were treated orally (po) with single or multiple doses of up to 400 mg/kg of D without any increases in SGPT or alterations in hepato-cellular architecture. To possibly enhance the hepatotoxicity of dantrolene, its biotransformation was altered by inhibiting acetylation, depleting glutathione, inducing biotransformation, and promoting reductive metabolism. None of the metabolic alterations elicited any toxicity of dantrolene. Hepatic microsomal incubations were used to detect the possible bioactivation and covalent binding of 14C-dantrolene. Analysis for covalent adducts found only 20-30 pmol bound/mg microsomal protein. Thus the suspected hepatotoxicity of dantrolene does not appear to be linked to its biotransformation or bioactivation. Additional studies will be necessary to clarify if other parameters are necessary for dantrolene to be a hepatotoxin.