This invention provides pharmaceutical uses for 2-methylene-19-nor-20(S)-1.alpha.,25-dihydroxyvitamin D.sub.3. This compound is characterized by high bone calcium mobilization activity demonstrating preferential activity on bone. This results in a novel therapeutic agent for the treatment and prophylaxis of diseases where bone formation is desired, particularly osteoporosis. This compound also increases both breaking strength and crushing strength of bones evidencing use in conjunction with bone replacement surgery such as hip and knee replacements, as well as use by normal subjects when high bone mass is desired.