1. In this study, cells derived from explants of human trabecular bone were treated with the anabolic steroid stanozolol in order to determine whether the potential therapeutic effect of this agent might be explained by direct effects on skeletal tissue. 2. Stanozolol at a concentration of 10(-10) mol/l to 10(-6) mol/l consistently stimulated the incorporation of [3H]thymidine into DNA of human bone cells and increased proliferation. 3. Stanozolol had variable effects on the expression of two other markers of the osteoblast phenotype, namely the bone-specific vitamin-K-dependent protein osteocalcin, and the enzyme alkaline phosphatase. Although stanozolol tended to increase the values, this was not seen in all experiments. 4. We conclude that human bone cells respond to stanozolol. The effects of this agent on cell proliferation may be important in understanding the mode of action of this drug in the treatment of osteopenic disorders.