Description: Newborn piglets weighing less than 1000 grams at birth are more susceptible to diseases and the negative infl uence of stress factors, slow progress, and therefore cause greater losses than heavier ones. Also, they are physiologically immature and establish postnatal metabolical mechanisms more slowly than suckling piglets of normal body mass. The aim of our research was to determine changes in the activity of some enzymes and concentrations of biocatalysts in the blood serum of suckling piglets. In this study 48 piglets were included: 24 animals with birth weight less than 1000 g (experimental group) and 24 littermates of the same sex with body mass of 1000 g and more (control group)