Chondrocytes obtained from tibiae of chick and rat at different developmental stages were cultured as three dimensional pellets in centrifuge tubes in medium containing different concentrations of serum for 28 days, to examine the changes in the alkaline phosphatase (ALP) activity as a marker of chondrocyte hypertrophy, changes in the calcium (Ca) contents as a marker of cartilage calcification and the development of hitological structure. Growth plate chondrocytes obtained from the proximal tibiae of 17.5 day chick embryos and 2.5 week old rats developed as a typical hypertrophied cartilage structure with rises in the ALP activity and the Ca contents, indicating the coincident results with the growth plate chondrocytes obtained from 3 or 4 week rabbits. Chondrocytes obtained from articulator cartilage in tibiae of 17.5 day chick embryos and 3 day newborn rats, which were used as more advanced differentiated chondrocytes, showed a partial hypertrophy and cartilageous structure with the high ALP activity and Ca contents in cell-pellets. Less differentiated prechondrocytes obtained from whole tibiae of 6.5day chick embryos showed a condensation of many fobroblastic cells and a poor hypertrophy in their histology of cell-pellets with a gradual rise in the ALP activity and low Ca contents. These results indicate that chondrocytes obtained from the tibial growth plate of chick and rat were suitable and useful materials for examining cellular and molecular process of cartilage differentiation in vitro.