Serial ultrasonographic examinations were daily performed on 12 Shih-tzu bitches from 15 days after ovulation until parturition to determine the time of first detection and ultrasonographic appearance of the fetal and extra-fetal structures and to determine the size of gestational structures. Gestational age was timed from the day of ovulation (day 0), which was estimated to occur when plasma progesterone concentration was first increased above 4.0 ng/ml. The gestational length in 12 Shih-tzu bitches was 62.1 (range:60-64) days. The initial detection of the fetal and extra-fetal structures were: gestational sac at days 19.2 (16-21); zonary placenta in the uterine wall at days 25.9 (24-28); yolk sac membrane at days 24.1 (22-26); amniotic membrane at days 26.6 (24-28); embryo initial detection at days 22.3 (21-24); heartbeat at days 23.8 (23-25); limb buds at days 29.3 (27-31); fetal movement at days 32.3 (31-34); stomach at days 32.6 (29-34); urinary bladder at days 33.1 (29-35); skeleton at days 35.9 (34-38) and kidney at days 45.8 (45-48).