Power Doppler (PD) is a recent color-Doppler Ultrasound (US)-technique, which allows to detect the presence of flow even in very small vessels, providing a sort of angiographic micromap. The aim of this study was to evaluate whether percutaneous ethanol injection (PEI) outcome might be improved by injecting the ethanol into the nodule under PD assistance. Thus, 14 patients affected with pretoxic (PTA) and 8 with toxic adenoma (TA) were submitted to this alternative tool. Before PEI, all patients were submitted to a careful endocrinological study, including an US-guided fine-needle biopsy in order to exclude the presence of malignancy. In addition, all the nodules were evaluated at PD-US and their vascular patterns were recorded on videotape and compared with those obtained after treatment. The procedure consisted of slow injection of sterile ethanol under direct PD-US control. The number of PEI sessions was 2.3+/-0.1 in PTA and 3.0+/-0.3 in TA. All patients were also evaluated 3, 6, 12 and 18 months after PEI. Successful therapy was considered when normalization of thyroid hormones and TSH was achieved together with the disappearance of nodular hyperactivity and complete recovery of extra-nodular tracer uptake at scintigraphy. PEI was tolerated very well by all patients. The most common side effect was a transient local or irradiated pain. All patients with PTA and 6 out of 8 patients with TA were successfully treated. In these cases, PD-US showed the progressive reduction of the intranodular blood flow, up to its extinction after 6-12 months, with the presence of little perilesional vascular spots. Nodular shrinkage was obtained in all patients (from 4.7+/-0.7 to 1.1+/-0.4 ml in PTA and from 21.0+/-2.8 to 6.2+/-1.6 ml in TA). In conclusion, PD assistance improves PEI procedure, since it allows to guide the ethanol injection towards the principal afferent vessels of the nodules and to monitor the diffusion and the effects of ethanol on nodular vascularization.