The IN/157 cell line was originally isolated from a human oligodendroglioma biopsy and has been used in recent years to study aspects of glioma cell biology. We established that IN/157 cells carry a relatively infrequent mutation at position three of codon 61 of the N-ras gene, suggesting that such a mutation may have contributed towards the genesis of the original tumour. However, the mutation was not detectable within the original paraffin-embedded glioma biopsy from which the cell line was supposedly derived. We thus considered the possibility that the cells had been contaminated by another cell line and, by means of DNA fingerprinting, have demonstrated that the contaminating cell line is the rhabdomyosarcoma line RD. We feel that this study makes several important points regarding experiments which make use of cell lines. We discuss the possible implications of contamination events with regard to erroneous conclusions about the biology of the cell lines and tumour types from which they supposedly derive. We also suggest ways in which future contamination-related errors can be minimized.