The Investigator ESSplex SE QS (Qiagen) amplifies sixteen STRs and Amelogenin. The reaction mix is supplemented with two quality sensors that are sensitive to inhibitors in the amplified samples. The quality sensors consist of a short fragment and a long fragment. Amplification of the long fragment is very sensitive to inhibitors, while the short fragment is very resistant to inhibitors. The kit sensitivity was tested with serial dilutions of high quality DNA. Full profiles were obtained down to 125. pg of DNA. The behaviour of the quality sensors was investigated by adding Hematin or Indigo Carmine to high quality DNA samples. The quality sensor peak height ratio increased and the peak heights of the longer fragments of the profiles decreased. The decreasing peak heights of the longer fragments are classical signs of DNA degradation. With artificially degraded DNA, the quality sensor peak height ratio was not affected. Investigations of 16 DNA extracts from stain samples from crime cases indicated that six of the samples were contaminated with PCR inhibitors and 10 of the samples contained degraded DNA.