The study showed that all five methods measured higher DNA concentrations than expected, based on the manufacturers' information. UV spectrometry, SYBR-Green dye staining, slot blot, and RB1 rt-PCR gave 39 percent, 27 percent, 11 percent, and 12 percent, respectively. The DNA preparations were quantified with the Quantifiler Human DNA Quantification kit in two experiments. The measured DNA concentrations with Quantifiler were 125 percent and 160 percent higher than expected from the manufacturers' information. When the Quantifiler human DNA standard (Raji cell line) was replaced by the commercial human DNA preparation G147A (Promega) in order to generate the DNA standard curve in Quantifiler Human DNA quantification kit, the DNA quantification results of the human DNA preparations were 31 percent higher than anticipated from the manufacturers' information. The findings show a calibration problem with the Quantifiler human DNA standard for its use with the Quantifiler Human DNA quantification kit. Possible reasons for this problem are discussed and a solution is suggested. The findings indicate the need for standard reference DNA material and standard methods for DNA quantification. The six DNA preparations mainly contained DNA of high molecular weight, although D3160, D3035, and human genomic DNA also contained a minor component of partly degraded DNA. There was no sign of RNA. 2 tables, 3 figures, and 16 references