Expression of bone morphogenetic proteins in human osteogenic and epithelial tumor cells. In addition to osteosarcomas some epithelial tumors also show bone induction, which is supposedly due to bone morphogenetic proteins (BMPs). However, the types of BMPs expressed in different kinds of tumors have not been studied extensively. In this study five human osteosarcoma and six human carcinoma cell lines were examined to investigate the bone induction and BMP mRNA expression. The cultured cells were transplanted in the subcutaneous tissue of athymic nude mice with or without diffusion chambers. Reverse transcription-polymerase chain reaction (RT-PCR) was used for the detection of BMP mRNAs. All osteosarcoma cell lines expressing all BMPs (BMP-1 to 7) examined, successfully formed bone or osteoid tissue irrespective of the use of a diffusion chamber. Bone formation was induced by diffusion chamber in an osteosarcoma cell line OST and a gastric adenocarcinoma cell line MKN45. OST cells lacked BMP-3 and 7, and MKN45 cells lacked BMP-3, 5 and 6. Our data suggest that BMP-3, 5, 6 and 7 are not always essential for bone induction in tumor cells.