Seventy patients with class 1 reticular varicosis of the lower extremities underwent sodium tetradecylsulfate compression sclerotherapy at a day cardiovascular hospital located in the city of Tambov. A liquid solution was used to treat 22 patients and a sclerosing foam (prepared by Tessari's method) in the remaining 48 ones. Upon appearance of clinical symptoms of thrombophlebitis within 7-60 days after sclerotherapy, venous contents were aspirated and subjected to cytological study. Macroscopically, the vascular contents looked like a homogeneous thick wine-coloured fluid rather than a thrombus (blood clot). Its microscopic study on day 7 showed the presence of a large number of variably altered erythrocytes, macrophages, and hemosiderophages suggesting activated phagocytosis. Isolated fibroblasts were detectable on day 10, fibrocytes on day 51, and hemosiderin after 2 months. In other words, no signs of thrombosis were apparent. The homogeneous thick fluid was detectable in the veins regardless of the time after sclerotherapy which gave reason to speak of the absence of any organization or recanalization even on days 50-60 post-treatment.