Medium-chain fatty acids (MCFA) are efficient antimicrobial compounds. The aim of this study was to evaluate the effect of caprylic acid (C8:0), and an oil containing triacylglycerols of caprylic and capric acid (C10:0), on growth rate of piglets and shedding of coccidia oocysts. Piglets, weaned at 28-32 days of age, were fed a basal diet (Group 1), the same diet supplemented with caprylic acid at 5 g/kg (Group 2), or supplemented with the MCFA-containing oil at 10 g/kg (Group 3). The experiment was carried out on a commercial farm and lasted for 3 weeks. In the course of this period piglets of groups 1, 2 and 3 gained on average 3.64, 4.98 and 3.95 kg, respectively. The effect of caprylic acid on weight gains was statistically significant (P<0.05). Almost all piglets were infected with Cryptosporidium parvum and some of them also with Isospora suis. In treated piglets, shedding of cryptosporidial oocysts was one week delayed and the patent period was shorter. This suggests that a certain coccidiostatic effect of MCFA exists.