Providing convincing evidence for the successful retrieval of aDNA-especially aDNA of human origin-is a demanding task, and even results that were obtained using extensive precautions have later been disputed and claimed to be due to contaminating modern DNA. The fundamental problem with analysis of ancient human DNA is the abundance of modern human DNA in most contemporary settings. Sampietro et al. recently showed that archaeological manipulation of human remains is a major source of contamination with modern DNA and Pruvost et al. showed that once skeletal remains are stored after excavation the authentic DNA seems to degrade rapidly. In the present work we have circumvented the above two obstacles by taking teeth from Viking remains at the excavation site at the moment the jaw was accessible. We removed the last layer of soil from the skulls and extracted premolars from the jaws wearing protective outfit. The results support the absence of prelaboratory contamination�Cin fact any contamination with human DNA, i.e. alignment of multiple cloned sequences showed no evidence of the existence of more than one mtDNA sequence from any given PI-103 subject, and the sequences did not match with any of the staffs ). The spectrum of haplotypes observed for the Viking BAY-60-7550 samples, i.e. ten different haplotypes for ten individuals, further strengthens the reliability of the results. Thus it would be highly unlikely that ten plausible haplotypes all fitting well within the phylogenetic tree would arise from the random combination of short authentic fragments and/or an undetected low background of contaminating DNA in the laboratory environment. The risk that post-mortem miscoding lesions in the template DNA lead to false conclusions about the true authentic sequence has been debated. The fewer template molecules being available for the PCR amplification the higher the risk of drawing wrong conclusions. Thus, the risk is considered to be low when the PCR is initiated with several hundred template molecules and as a rule of the thumb reliable DNA sequences may be obtained from a single PCR if more than 1,000 starting molecules are present. In the present work extracts of ancient DNA contained between 4,720 and 375,120 molecules, i.e. 177 ancient templates were present in PCR reactions with the most dilute extract and thousands of molecules were available with the more concentrated extracts. Given that the present results are all based on multiple clones from PCRs of extracts from at least two teeth the likelihood of the ancient sequences presented here being due to artefacts seems very low. Research on the biological basis of SZ and other neuropsychiatric disorders has been hampered by the inaccessibility of the human brain. However, the discovery of iPSC technology has the potential to address this problem by providing investigators with patient-specific neurons that can be used for disease modeling.