Estrogen sulfatase and sulfotransferase (EST) activities are present in breast cancer tissues but there are no reports on EST in cancerous bone cells, We incubated [H-3]estradiol-17 beta with cells from a canine osteosarcoma D17 line for periods up to 24 h, Radioactive steroids were recovered from the media and separated into unconjugated and conjugated fractions using Sep-Pak C18 cartridges. The conjugate fraction was solvolyzed and the resulting free steroids were obtained from a second C18 cartridge. Little metabolism was apparent in 4 h of incubation, but by 24 h as much as one half of the radioactivity was seen in the conjugate fraction. Most of the conjugates were recovered as sulfates in all three experiments. HPLC profiles showed a limited metabolism of estradiol to other compounds except for estrone, which was clearly present in both free and sulfate fractions. These results suggest that EST may have a role in the local metabolism Of estrogens in bone,