Avermectin endectocides are very effective and safe veterinary drugs, when used at recommended doses. Adverse reactions are described in some species and breeds of animals. In this study, the effects of therapeutic doses of abamectin and doramectin on some haematological and biochemical parameters in Istrian Pramenka sheep are discussed. In the pilot trial, we compared selected haematological and blood biochemical parameters of an experimental sheep flock (40 sheep) with the reference values. Then, two groups of 12 sheep (and their suckling lambs) were chosen from the experimental sheep flock. Each group was subdivided into a control (six animals) and treated (six sheep and their six suckling lambs) groups. We compared haematological and biochemical parameters between control and treated group before subcutaneous administration of abamectin or doramectin (0.2 mg/kg b.w.) and on days 15 and 42 after treatment. In addition, animals were observed for neurological signs. We detected some significant differences (P < 0.05) in some haematological and biochemical parameters between control and treated animals, but none of them appeared to be of clinical importance. No neurological symptoms were observed. Therefore, abamectin and doramectin might be well tolerated in Istrian Pramenka sheep.