Induction of hepatic metallothionein (MT) by urethane (ethyl carbamate) was characterized. Male CF-1 mice were treated with urethane (0, 0.5, 1.0, 1.5, and 2 g/kg; ip) and 18 hr later hepatic MT concentrations were determined with the Cd-hemoglobin radioassay. Urethane (1 g/kg and higher) significantly increased hepatic MT levels, resulting in a 14-fold increase after 2 g/kg. Time-course experiments indicated that MT levels were increased significantly at 6 hr after administration of urethane (1.5 g/kg) and reached a maximum between 12 and 24 hr. Gel filtration, anion-exchange chromatography, and ultraviolet spectral analysis were used to characterize the protein induced by urethane. Pretreatment with actinomycin-D prevented induction of MT by urethane. Administration of equimolar dosages (20 mmol/kg) of urethane, N-hydroxyurethane, and methyl carbamate indicated that urethane and N-hydroxyurethane induce MT but that methyl carbamate does not. MT induction was also not observed with other commonly used anesthetics (pentobarbital and phenobarbital). In conclusion, urethane induces hepatic MT but this effect is not related to its anesthetic action, nor is it a common property of all carbamates.