Pharmacokinetics of eprinomectin (EPR) were studied in blood plasma and milk in two groups of six Istrian Pramenka dairy sheep and their suckling lambs following pour-on administration of EPR to ewes at dose levels of 0.5 and 1mg/kg. Maximum concentration in plasma was 2.22 and 5.25 microg/l, and AUC was 13.6 and 33.7 microg day/l for the 0.5 and 1.0mg/kg dose, respectively. These results indicate that drug exposure with a dose of 0.5mg/kg, which is commonly used in cattle, may be subtherapeutic. The concentration time course in milk paralleled plasma concentrations. In the dose range studied, linear pharmacokinetics of EPR were demonstrated. Milk-to-plasma AUC ratio was 0.79+/-0.12 and 1.12+/-0.43; the fraction of dose recovered in milk was 0.037+/-0.011 and 0.058+/-0.027% for the low and high dose, respectively. Maximum residual levels in milk were below the maximum acceptable level of 20 microg/kg; however, EPR was detected in all samples investigated. Despite low permeability in milk, AUC in plasma of suckling lambs was between 20 and 30% of the AUC in plasma of ewes.