Histological and histochemical research of preventive action of “Trofeparin” ointment and medicines of comparison — ointment with heparin and ointment with metiluracil — under thrombophlebitis in experimental rats was conducted. “Trofeparin” ointment reduced vein walls inflammation and prevented blood clot formation, and these characteristics were more pronounced as compared to medicines of comparison: ointment with heparin and ointment with metiluracil.