Transdermal 17 beta-oestradiol administration (17 beta-E2), used mainly in menopausal women, allows a continuous 17 beta-E2 delivery through the skin into the systemic circulation, avoiding intestinal and hepatic passage. In order to explore whether transdermal 17 beta-E2 could be used for the induction of puberty, 17 beta-E2 patches with low dose delivery were administered in nine prepubertal girls with Turner syndrome (bone age greater than 10.5 years) for a mean period of 2.2 years. Treatment schedule: 5 micrograms/day for 6-9 months, 10 micrograms/day for 6-9 months, 25 micrograms/day for long-term substitution; addition of cyclic gestagen p.o. after 18-24 months. Breast development started within 3 months of therapy and menstruation occurred after 2 years. Growth rate increased from 3.2 to 5.0 cm/year during the 1st year of therapy, height prediction did not change. Serum oestradiol (E2) and urinary E2 conjugates increased proportionally with 17 beta-E2 doses, serum oestrone (E1) rose much less. The possibility to imitate time course, clinical events and hormonal changes of normal puberty, the absence of adverse drug reactions and the excellent acceptance and easy mode of application suggest that transdermal 17 beta-E2 is optimally suited for hormonal substitution in girls with hypogonadism.