Studies from our laboratory revealed that direct application of physical strain (PS) to cultured bone cells stimulated synthesis of prostaglandin E₂ (PGE₂) in a specific population of cells. We found that PGE₂ induced the cellular production of cAMP in several bone cell types, whereas the induction of DNA synthesis was limited to osteoblastlike cells. Indirect evidence indicated that PS induced the osteoblastlike cells to synthesize PGE₂. Other cell types, for example, chondrocytes, when activated by PS, can be induced to produce cAMP and induced DNA synthesis not mediated by PGE₂. We have also found that electric stimulation of different populations of bone cells is specifically induced by a certain intensity of the electric field. It seems that electric stimulus circumvents the PGE₂ effect and triggers the adenyl cyclase system in the cell directly. The electric field also induces DNA synthesis not via PGE₂ production.