Using morphological and biochemical (Western blot and cell fractionation) methods, we investigated whether peroxisomes are present in human extravillous trophoblast cells. Immortalized extravillous trophoblast cells (TCL-1) were incubated in the presence or absence of 0.5 mM clofibric acid for 3 d. In immunofluorescence staining of trophoblast cells with antibodies anti-catalase and anti-acyl-CoA oxidase (marker enzymes of peroxisomes), electron microscopy and immunoelectron microscopy, peroxisomes were detected in the cells. The size and number of peroxisomes in the trophoblast cells were smaller than those in rat liver. The number of peroxisomes was increased by clofibric acid. In Western blot experiment with antibodies anti-peroxisomal enzymes of β-oxidation system, densitometric analysis revealed approximately two fold increase in staining by clofibric acid. When we performed cell fractionation experiment using catalase as one of the peroxisomal marker enzymes, the highest activity of catalase was found in the light mitochondrial fraction. Specific activity of catalase in the light mitochondrial fraction was significantly increased to about 1.3 times higher than the control value by clofibric acid treatment. Upon Nycodenz density gradient centrifugation, the catalase activity was concentrated in the density fraction around 1.14—1.15. These findings suggest that microperoxisomes, which have a density smaller than those of rat hepatic peroxisomes, do exist in human extravillous trophoblast cells. It may also be possible to proliferate human peroxisomes in limited quantities using peroxisome proliferator of rodents.