Serial ultrasonographic examinations were daily performed on 11 bitches (5 Maltese and 3 Yorkshire terrier) from day 15 until parturition to determine the time of Sift detection and ultrasonographic appearance of the fetal and extra-fetal structures. Gestational age was timed from the day of ovulation (day 0), which was estimated to occur when p18sma progesterone concentration was first increased above 4.0 ng/ml. The gestational length in 8 bitches was 61.5 (range: 60-64) days. The initial detection time of fetal and extra-fetal structures were: gestational sac at days 20.5 (18-23); zonary placenta in the uterine wall at days 25.4 (24-30); yolk sac membrane at days 25,5 (23-37); amniotic mombrane at days 28.7 (25-32); embryo initial detection at days 23.3 (20-26); fetal heartbeat at days 23.9 (21-27); fetal movement at days 31.3 (26-34); limb buds at days 32.1 (29-35); rotomarh at days 35.3 (32-40); urinary bladder at days 35.6 (33-39); skeleton at days 37.8 (37- 40) and kidney at days 45.3 (41-49), respectively.