The purpose of this study was to determine the pharmacokinetic interaction between ivermectin (0.4 mg/kg) and praziquantel (10 mg/kg) administered either alone or co-administered to dogs after oral treatment. Twelve healthy cross-bred dogs (weighing 18-21 kg, aged 1-3 years) were allocated randomly into two groups of six dogs (four females, two males) each. In first group, the tablet forms of praziquantel and ivermectin were administered using a crossover design with a 15-day washout period, respectively. Second group received tablet form of ivermectin plus praziquantel. The plasma concentrations of ivermectin and praziquantel were determined by high-performance liquid chromatography using a fluorescence and ultraviolet detector, respectively. The pharmacokinetic parameters of ivermectin following oral alone-administration were as follows: elimination half-life (t(1/2 lambda z)) 110 +/- 11.06 hr, area under the plasma concentration-time curve (AUC(0-infinity)) 7,805 +/- 1,768 hr(.)ng/ml, maximum concentration (C-max) 137 +/- 48.09 ng/ml, and time to reach C-max (T-max) 14.0 +/- 4.90 hr. The pharmacokinetic parameters of praziquantel following oral alone-administration were as follows: t(1/2 lambda z) 7.39 +/- 3.86 hr, AUC(0-infinity) 4,301 +/- 1,253 hr(.)ng/ml, C-max 897 +/- 245 ng/ml, and T-max 5.33 +/- 0.82 hr. The pharmacokinetics of ivermectin and praziquantel were not changed, except T-max of praziquantel in the combined group. In conclusion, the combined formulation of ivermectin and praziquantel can be preferred in the treatment and prevention of diseases caused by susceptible parasites in dogs because no pharmacokinetic interaction was determined between them.