This research indicates that the numerical value of the emptying of somatic cells as a result of the effect of time of day cannot be demonstrated and interval difference less than 2 hours between milking does not significantly influence the formation of somatic cells and their absolute quantity. <br><br> Moreover it was confirmed that subclinical mastitis also occurs in individual udder quarters of healthy qualified cows producing bulk milk with somatic cell count below 400 thousand / ml. Udder quarter with mastitis was found in 15,2 % of cows of the tested stock realising this production, which can be considered a significant proportion and is a justification for eliminating and taking udder health care of these animals