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The pharmacokinetics, metabolism and excretion of monoethyl phthalate (MEP) and diethyl phthalate (DEP) were compared after intravenous or oral administration of [14C]MEP or [14C]DEP in juvenile beagle dogs. Four male juvenile beagle dogs were treated with a single oral or bolus intravenous dose of either [14C]MEP or [14C]DEP (164 μg/kg). The absorption, metabolism, excretion and pharmacokinetics of [14C]MEP and [14C]DEP were nearly identical. [14C]DEP was rapidly and nearly completely metabolized to [14C]MEP following either intravenous or oral administration. [14C]MEP and[14C]DEP were rapidly absorbed, the elimination half-life was estimated to be 1 hour. Approximately 90%–96% of the dose was excreted in urine with 2%–3% of the dose in faeces. MEP accounted for the majority of the dose in plasma and urine; in addition, three minor metabolites (M1, M2 and M3) were detected. The minor metabolites were neither phthalic acid nor glucuronide/sulfate conjugates. The nearly identical metabolism and pharmacokinetics of MEP and DEP in juvenile dogs justifies the use of DEP toxicity data in the risk assessment of MEP exposure. [ABSTRACT FROM AUTHOR]