OBJECTIVE: To study the effects of pulsed ultrasound (PUS) and pulsed electromagnetic fields (PEMF) on the secretion of extracellular matrix from a culture complex during in vitro chondrogenesis. METHODS: All the rat bone marrow mesen- chymal stem cell pellets were cultured in achondrogenic medium. Different intensities of PUS (100, 150, and 200 mW · cm⁻²) and PEMF (1, 2, and 5 mT) were applied to the cell pellets for 2 weeks. Group N was cultured without PUS and PEMF stimu- lation as control. The culture medium was collected after 2 weeks of culture. Enzyme-linked immunosorbent assay (ELISA) was used to detect the type of collagen and glycosaminoglycan (GAG) in the culture medium. RESULTS: PUS increased the secreting-type collagen and GAG from cell pellets compared with group N (P < 0.05), whereas there was no difference in different intensities (P > 0.05). PEMF had no significant effect on the secretion of the type of collagen (P > 0.05). A PEMF of 1 mT had no significant effect on the secretion of GAG (P > 0.05). A PEMF 2 and 5 mT decreased the secretion of GAG (P < 0.05). CONCLUSION: To prevent the secretary of extracellular matrix may play a role in chondrogenic effect of PEMF.