SV40 footprints were investigated by PCR in normal human tissues and tumours of different histotypes, followed by Southern blot hybridization with a specific internal oligoprobe for SV40 DNA. Specific SV40 amplification products were detected at high prevalence in primary human brain tumours: 83% of choroid plexus papillomas, 75% ependymomas, 47% astrocytomas and 37% glioblastomas. SV40 footprints were also revealed in primary bone tumours: 35% osteosarcomas and Ewing's tumours. Positive normal tissue samples ranged from 45% of sperm fluids to 8% of brain tissue. Normal bone tissue specimens were SV40 negative. These results indicate that SV40 is associated with human brain and bone neoplasms, whereas normal bone and brain tissues were either SV40 negative or positive at low grade. SV40 footprints were found in other normal samples such as PBC, B- and T-lymphocytes and sperm fluids, indicating that SV40 is latent in these cells. Therefore, these cells may be vectors of SV40 in other host tissues and may spread SV40 infection by blood transfusion and sexual transmission in the human population.