Efficient gene delivery of a baculovirus-derived vector (BV-p53-lacZ) to a human osteogenic sarcoma cell line, Saos-2, was serendipitously found while evaluating the vector for gene delivery to human p53-null tumour cells in a previous study. Therefore, we investigated other human, rat and mouse osteogenic sarcoma and other types of tumour cell lines for transduction efficiency via baculovirus vectors containing a lacZ reporter gene under the control of either a cytomegalovirus or Rous sarcoma virus promoter. The expression of beta-galactosidase protein, assessed by X-Gal staining and beta-galactosidase ELISA, demonstrated an extremely high level of transduction efficiency in some osteogenic sarcoma cell lines, such as U-2OS, Saos-2 and Saos-LM2. These human osteogenic sarcoma cell lines showed levels of beta-galactosidase expression 5-40 times greater than HepG2 cells, which were previously thought to be the mammalian cells most susceptible to baculovirus-mediated gene delivery. The level of acetylated histone proteins in these tumour lines did not correlate well with the high level of reporter gene expression. These results strongly suggest that some osteogenic sarcoma cells are highly susceptible to baculovirus-mediated gene delivery and that a baculovirus-derived vector is an efficient gene delivery vehicle into human osteogenic sarcoma cells.