Following PGF2administration during the early or lateluteal phase, the radiotelemetry performed at 90% effi-ciency (45/50 detected in estrus) and 100% accuracy (45/45ovulations). There was no mounting behavior in the fiveheifers whose estrus was not detected by radioteleme-try, although these heifers had silent estrus, as confirmedby ovulation (10%; n = 5/50 not detected in estrus). Theradiotelemetry efficiency for the detection of estrus wassimilar (P > 0.05) for PGF2treatment provided duringthe early (90.9%; 30/33) or late (88.2%; 15/17) lutealphase.