The ideal preparation for estrogen replacement therapy has been the object of intensive research for decades, and the search continues. More than 40 new products are in development in the United States, the United Kingdom, and Europe. Most are transdermal, which reflects the growing acceptance of patch technology at a time when the overwhelming majority of women who use estrogen replacement take oral formulations. Most of the new oral formulations are a combination of estrogen and progestin. Aspects of transdermal and oral estrogen are discussed, including the advantages and disadvantages for use in women with concomitant medical conditions.