Animals spontaneously developing lupus-like autoimmune pathology (SLE) are very promising models to study the mechanisms of natural abzymes (Abzs) generation and their role in etiology and pathogenesis of autoimmune diseases, but Abzs from the sera of animals remain virtually unstudied. In this work, electrophoretically homogeneous IgGs were isolated from the sera of MRL/MpJ-lpr mice. It was shown for the first time that amylase activity is an intrinsic property of antibodies (Abs) and their isolated heavy and light chains. Various markers of SLE pathology (proteinuria, enhanced concentration of anti-DNA Abs) increased with spontaneous development of SLE and especially after animal immunization, correlating with the increase in Abz relative amylase activity. The highest amylase activity was found in the sera Abs of healthy mice after delivery and at the beginning of lactation; this was not correlated with markers of mouse SLE but supports the idea that pregnancy could "activate" or "trigger" autoimmune-like manifestations and Abzs production in healthy mammals. The possible differences in mechanisms of Abzs production in lactating mice and animals developing SLE are discussed.