Using a technique which makes use of digitonin to selectively permeabilize the cell, we established earlier that in chorionic villus fibroblasts catalase is contained in subcellular particles (peroxisomes) as in skin fibroblasts (Wanders et al., 1986). Based upon this finding was have now developed a sensitive method which allows direct visualization of peroxisomes in cultured chorionic villus fibroblasts by immunofluorescence microscopy using an anti-(catalase) antiserum, thus providing a simple method for prenatal diagnosis of Zellweger syndrome or any of the other peroxisome deficiency disorders.