Thirty patients with uterine leiomyomas which were treated by LITT were evaluated histologically, and biologically for oestrogen receptors and epidermal growth factor, at the time of treatment and often subsequently, up to three years later. Three lasers were evaluated: 5W were found to be necessary to produce a lesion 10mm in diameter when the Nd:YAG laser was employed for 500 seconds. The KTP laser alone, using the same number of Joules, produced a larger volume of vaporization and coagulation.However, the most striking effect was achieved with a combination of KTP and YAG. The diode laser alone produced a lesion equivalent to that of the Nd:YAG laser. However, when employed with a fiber splitter and four fibers, each delivering a power of 4W, the volume of necrosis around each fiber was doubled. Finally, the diode laser, when fitted with a diffuser fiber, produced a lesion three times larger than that of the Nd:YAG laser, and there was no char. Histochemical study of oestrogen receptors and immunohistochemical study of epidermal growth factor in the lesions produced by LITT have shown that they are destroyed.