Chorionic villus sampling (CVS) has proved to be an elegant and safe technique for prenatal diagnosis of genetic diseases during the first trimester of pregnancy. Despite a number of obvious advantages, the wide application of direct cytogenetic analysis of CVS has been hampered by serious technical problems involving large numbers of incomplete metaphases and poor chromosome morphology. A chromosome preparation technique direct from CVS has been devised which involves modifications in the hypotonic and dissociation stages. It yielded satisfactory results in fifteen samples within 24 h of sampling. It is suggested that this simple, modified technique can provide complete chromosomal analysis within a short time for prenatal diagnosis of genetic diseases, and may be used as a routine method in cytogenetic laboratories.