Prolactin (PRL), a pituitary hormone, exerts a significant influence on reproductive functions in dogs and non-domestic canines (wolf, fox, coyote et al.). Pseudopregnancy is obligatory for all non-pregnant females in these species, which ensures their capability of caring for and even nursing a litter. This is caused by a PRL rise during the second half of pregnancy, which in the dog is quantitatively equal in pregnant and overt pseudopregnant animals; in covert pseudopregnant bitches this rise in PRL is significantly lower. Consequently, these animals do not show the enlargement of the mammary glands and their secretions, and the typical distorted behaviour seen in overtly-pseudopregnant bitches. The use of potent PRL- inhibitors, mostly dopamine agonists like bromocriptine, metergoline and cabergoline, has revealed that PRL is the luteotropic hormone from day 30 of pregnancy onward and that PRL is essential for the preparation of the mammary glands for lactation, the commencement of lactation and its maintenance, and for the maternal (and paternal) care of the litter. Hence, these PRL-inhibitors are in use for induction of abortion after mid-gestation, for the treatment of overt pseudopregnancies and to stop unwanted lactation. Male and female dogs and wolves show almost identical seasonal changes in PRL blood concentrations with peak levels before mid-year and the nadir just before the year's end. In non-domestic canines with one oestrus annually in late winter/early spring the annual PRL peak coincides with the need to care for the litter late in spring/ early in summer. Females that were pregnant or pseudopregnant are ready to nurse and take care of whelps and simultaneously, the seasonally peaking PRL blood concentrations seem to smooth over social tensions between males and ensure their essential participation in the care of the litter. In the bitch, pseudopregnancy has become an atavism and over-production of PRL causes anoestrus. Hence, PRL-inhibitors can be used for the treatment of anoestrus and for shortening the oestrous interval as well. The pseudopregnant cat does not form additional PRL, but in the pregnant cat, PRL is an essential luteotropin during the second half of pregnancy. Hence, cats can be aborted during this time period with PRL-inhibitors and these compounds are useful in order to stop lactation.