The objective of this study was to identify selected blood immunological and biochemical parameters in horses infected with Cyathostominae before and after treatment with ivermectin. Fecal samples were collected before ivermectin treatment and on days 1, 2, 3,4,10, 20, 30, 40, 50, 60, and 75 after drug administration. Blood was sampled on the same days to determine levels of total protein, γ-globulin, ceruloplasmin, and lysozyme activity. Eggs and dead parasites were excreted until day 3 postivermectin treatment. The reappearance of eggs was observed in 1 horse on day 50, and on day 75 in the remaining animals. Before treatment, total protein levels were measured at 53.2 g/L on average, and a decrease was noted until day 3 after treatment, with minor fluctuations on the following days. The highest γ-globulin concentrations of 14.1 g/L were reported on day 10 after treatment. Ceruloplasmin levels were determined at 74 IU before treatment, and a significant increase to 106 IU was observed on day 40. Lysozyme activity before ivermectin treatment reached 2.77 mL/L on average, and a significant 2-fold increase to 6.85 mg/L was reported on day 75.