Abstract: An investigation on the blood parameters of fifteen Friesian young calves 3-4 weeks old at Aber Farm (UK), failed to demonstrate any differences in packed cell volume (PCV) and differential leucocyte counts (DLC) were seen between positive and negative cases, either when infected with pure or mixed infections of Cryptosporidium and Eimeria oocysts. The packed cell volume and differential leucocyte counts falling within normal range for uninfected calves.