A human chondrosarcoma cell line has been established from an aggressive chondrosarcoma. The cells grow in a monolayer culture (doubting time: 2 days) and form aggregates. The aggregates consist of a rim of cells surrounding a hollow core. The cell line exhibits a unique pattern of mRNA expression with several molecules characteristic of the chondrocyte phenotype. Consistent with the chondrocyte phenotype, mRNAs encoding types IX and XI collagens were present along with an abundant expression of mRNAs encoding the core protein of the cartilage proteoglycans biglycan and aggrecan. No expression of mRNAs encoding types I or II fibrillar collagens or the proteoglycan decorin was observed. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of [35S]sulfate-radiolabeled material confirmed the translation of proteoglycans containing glycosaminoglycan chains. The expression of molecules that contribute to cartilage development and tumorigenesis was examined. The cell line produces abundant mRNA that encodes transforming growth factor-β1, a member of a family of cartilage and bone inductive proteins. The expression of mRNA encoding two proteins associated specifically with chondrogenesis was detected: Cart-1, a homeobox protein involved in cartilage differentiation, and CD-RAP, a secreted molecule restricted under normal conditions to differentiating chondrocytes and cartilage. Overexpression of p53, a tumor-suppressor gene, was detected. DNA analysis revealed a loss of heterozygosity at the chromosomal locus encoding p53, with the deletion of one p53 allele and the mutation of the remaining allele in both the parent tumor and the cell line. The malignant chondrosarcoma phenotype may be related to the unique gene expression pattern that is characteristic in many ways of differentiating chondroblasts, as well as to the inactivation of the p53 function that could contribute to the proliferative capacity of the cell line. This cell line may serve as a biological model for further investigation of the etiology of human chondrosarcomas and for the synthesis and regulation of cartilage-specific genes.