Animal domestication is a natural selection experiment the important result of which is a great increase in the rate of appearance of new forms and in the wild range of variation of organisms. Analysing different aspects of this problem, D.K. Belyaev has came to a hypothesis that the morphological and physiological reorganisation of domestic animals has been going by the way of unconscious selection of animals on their behaviour, carried out by person at the very first stages of domestication (Belyaev, 1979). To testify this hypothesis, a population of tame silver foxes has been produced in long-term selection for lack of aggression and fear towards humans (domestic behaviour) at the Institute of Cytology and Genetics in Novosibirsk, Russia. In the process of selection the genetic transformation of behaviour and morphology, and physiological functions has been observed (Trut, 1999). In particular, selected animals show no aggressiveness to man, behave amicably towards humans and have some changes in the coat colour and body constitution (Trut, 1999). The important part of Belyaev’s hypothesis was the assumption that selection for domestic behaviour could affect the reproductive function, in particular the pituitary-gonadal axis controlling reproduction and fertility. The aim of this study was to obtain information about possible changes in reproduction between control (C) and domesticated (D) vixens. Reproductive performance, potential fertility, embryonic mortality and fetal viability were analysed for vixens from domesticated and control population. In addition, plasma progesterone concentrations were determined in selected and control females during pregnancy.