In order to develop an in vitro model allowing investigation of the long-term effects of hormones and other agents on peroxisomes in liver cells, we measured the activity of a series of peroxisomal enzyme activities in HepG2 cells, a proliferating cell line derived from a human hepatoblastoma. The results obtained show that although in absolute terms peroxisomal enzyme activities are lower in HepG2 cells as compared to human liver, relative activities were comparable in HepG2 and human liver, respectively. Furthermore, it is shown that peroxisomes can easily be isolated from HepG2 cells using density gradient centrifugation. It is concluded that HepG2 cells represent a good model system to study the characteristic (long-term) regulation and control of metabolism of human liver peroxisomes.