Imidocarb residues in liver and muscle were measured by HPLC after a single therapeutic dose to cattle (3 mg imidocarb dipropionate kg-1). Imidocarb and 7-ethoxycoumarin metabolism were compared in three different in vitro systems prepared from bovine liver: cultures of hepatocyte monolayers, precision-cut liver slices, and microsomes. The potential hepatotoxicity of imidocarb residues was tested on hepatocyte monolayers and assessed using the neutral red and lactate dehydrogenase leakage assays. The concentration of imidocarb (mean +/- SD) decreased between days 14 and 224 after treatment from 5.40 +/- 0.61 to 0.12 +/- 0.01 and from 1.05 +/- 0.31 to 0.06 +/- 0.02 microgram g-1 in liver and muscle, respectively. The depletion kinetics of imidocarb fitted a two-compartment model with alpha- and beta-phase half-lives of 31.7 and 48.5 days in liver and 34.9 and 120.7 days in muscle, respectively. Imidocarb metabolites were not detected in any in vitro system. 7-Ethoxycoumarin metabolism was found in all in vitro systems; the predominant metabolite produced by hepatocyte and liver slice cultures was umbelliferone glucuronide. Cytotoxicity of imidocarb (100 microM) to hepatocyte monolayers was maximal after 72 hr treatment and dose-dependent above 10 microM imidocarb. It is most likely that the hepatotoxicity of imidocarb is caused by the parent compound, because no evidence for imidocarb metabolism was found.