DNA can be extracted from hair shafts and hair roots. The content of DNA in hairs is usually limited: the root end of hairs may contain 0.5 micrograms DNA and shed hairs contain less than 10 ng DNA. DNA analysis with restriction fragment length polymorphism (RFLP) requires microgram amounts of DNA. Such DNA cannot be obtained from such samples as single hairs or blood stains. Even with a little amount of DNA, specific genes of DNA can be greatly amplified to more than 10(6)-fold in vitro by polymerase chain reaction (PCR). We extracted the DNA from a half, 1, and 2 hair roots and 4 hair shafts and amplified the DNA with primer pairs (5'-GCACCATTCTAAAGAATAAC-3', 5'-GGATTGTAGCTGCTATTAGC-3') of the beta-globin gene, covering part sequences of the IVS-2 region by using the polymerase chain reaction for 50 cycles. The electrophoresis of the PCR product revealed a 131 base pairs band. Finally, we hybridized the PCR product with an IVS-2 probe (5'-GGGTTAAGGCAATAGCAAT-3'). A fragment of the IVS-2 extending from nucleotide 612 to 742 of the beta-globin gene can be demonstrated in the slot blot filter of hair roots and hair shafts, but not in the 1 microgram of blood which was not amplified by PCR. Detection of the beta-globin gene from single hairs by using the PCR may be useful for the diagnosis of thalassemia from single hairs.