Because of the recent advances in the acquisition of human materials for research in addition to the value in the evaluation of the mutagenicity in humans, the use of human S9 fractions in the Ames test is starting to attract attention. However, until recently, available data on the mutagenicity with human S9 fractions has been limited. We have thus accumulated a large and extensive body of data on the Ames test with human S9 fractions during the last 5 years. In this report, these data are reviewed, and the utility of the human S9 fractions in mutagenicity testing systems is discussed.