Efficient growth inhibition of human osteosarcoma cells using a peptide derived from the MDM-2-binding site of p53. Protein transduction therapy is a promising alternative to gene therapy, but has not previously been investigated for osteosarcoma. We here demonstrate efficient growth inhibition of human osteosarcoma cells using a p53 peptide. Our result suggests that protein transduction therapy has significant potential as a novel therapeutic approach for osteosarcoma.