The authors describe the technique used in the treatment of autonomously functioning thyroid nodules by percutaneous ethanol injection (PEI). They illustrate the free-hand technique followed in their hospital from January 1990 to October 1992 in a group of 25 patients. Results, advantages and disadvantages of this technique are reported and compared with the ultrasound-guided technique. In the latter, widely used, the needle is positioned in the target nodule by means of an ultrasound probe with a specially designed guiding device which forces the needle in the correct direction. This makes the manoeuver rapid and safe as the needle tip can be easily visualized. In this case, the most important drawback lies in the impossibility of changing the ultrasound scanning plane during the ethanol injection as the probe and the needle are fast together. So the correct spreading modality of ethanol inside the tissue is not completely checked. Another disadvantage is the cost of disposable guiding device necessary in order to avoid contamination. On the other side, in the free-hand technique the needle is aimed at the nodule and inserted during an ultrasound examination without restrain on the probe movements. In this way, it is possible to focus the attention on the critical structures to prevent their damage stopping ethanol injection as soon as a seepage outside the thyroid occurs. Furthermore, this technique is particularly inexpensive as a standard probe is used and the risk of contamination can be avoided by just wrapping the probe with a sterline plastic film.(ABSTRACT TRUNCATED AT 250 WORDS)