Impedance plethysmography (IPG) and the Doppler ultrasonographic probe were used to assess whether thrombophlebitis, initiated by injection of a sclerosant into superficial varicose veins, extended to involve the deep veins of the leg. Sixty-seven legs were treated with compression sclerotherapy in 50 patients (26 men, 24 women) whose mean age was 53 years. Indications for this therapy were unacceptable appearance (n = 37), pain (n = 13), cramps (n = 11), and stasis ulcer (n = 6). Each leg received an average of six injections (range, three to 11) of 0.5 mL of sodium tetradecyl sulfate. Blood flow in the deep veins was studied immediately before injection of the sclerosant and one week and two weeks afterward. In each leg, no change in either of these studies was found at one and two weeks following injection treatment. In nine extremities, delayed venous emptying was found on IPG. This persisted after sclerosis and was interpreted as evidence of a previous deep vein thrombosis.