During late pregnancy (greater than 50 days) the pattern of uterine electrical activity is characterized by episodes of activity lasting 3-10 min and recurring at a low frequency (maximum 2.5/h). During the last 7 days before delivery there is a progressive qualitative change in activity which is correlated with the decrease in plasma progesterone concentration. Together with significant quantitative changes in uterine activity which occur during the last 24 h before parturition and after the sharp fall in progesterone concentration this suggests that progesterone plays a crucial role in the process of parturition in the bitch. Experiments with a calcium-channel antagonist have demonstrated the important role of Ca2+ ions in uterine contractility in dogs, but further investigations will be necessary to illustrate the clinical significance of hypocalcaemia in relation to primary uterine inertia. By marking all fetuses in utero before term by means of a radio-opaque substance, it was demonstrated that, when one or more pups were left in each uterine horn after birth of a pup, 78.2% of the pups were expelled from the contralateral horn. Assessment of the blood gas and acid-base status in spontaneously born puppies indicated that the initial state of acidosis is more severe than in several other domestic species. A mild to severe combined respiratory-metabolic acidosis occurs in almost every newborn puppy.