The present study was carried out on a total number of 45 multiparous Holstein - Friesian dairy cows under field conditions. Cows were visited twice antiparturn and daily postpartum for 3 successive months for observation of ovarian activity between 7: 30 and 9:30 at morning and between 6: 30 and 7: 30 in the evening. Body conditions cores was measured and blood and milk samples were taken. All cows were gynaecology examined and parameters of reproduction were determined. The onset of the first ovarian activity was specified by rectal palpation and by ultrasonograph. Cows starting postpartum ovarian activity within 30 days were considered early responders (ER) and cow starting postpartum ovarian activity later (more than 30 days) was considered late responders (LR). Ketone bodies measured were B hydroxy butyrate in serum and acetoacetate and acetone in serum and milk. Blood serum and milk ketone body concentrations during the first 6 weeks of lactation were higher in LR than in ER. Ketone bodies from calving to fist ovarian activity were better for prediction of the onset of cycle. Milk acetone and serum B- hydroxy butyrate concentrations provided the most reliable information of all ketone bodies with regard to resumption of ovarian activity.