The present study was carried out on a total number of 45 multiparous Holstien-Friesian dairy cows under field conditions. Cows were visited twice antipartum 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 condition scores were measured and blood and milk samples were taken. All cows were gynecology examined and parameters of reproduction were determined. The onset of the first ovarian activity was specified by rectal palpation and by ultrasonography. Cows starting postpartum ovarian activity within 30 days were considered early responders (ER) and cows starting postpartum ovarian activity later (more than 30 days) were considered late responders (LR). Ketone bodies measured were B-hydroxybutyrate 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 first ovarian activity were better for prediction of the onset of estrus cycle. Milk acetone and serum B- hydroxybutyrate concentrations provided the most reliable information of all ketone bodies with regard to resumption of ovarian activity especially when the other facilities like hormonal assay and ultrasonography were out of question under field condition.