Abstract. 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. 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