A method was developed to visualize individual DNA molecules in solution under a fluorescent microscope connected to a highly sensitive video camera. DNA stained with a fluorescent dye, DAPI, revealed thin extended filaments, thicker filaments and rapidly transforming folded structures dependent upon the solution conditions. Structural transitions were observed and recorded as video images. Our observations indicated the possibility that DNA has the ability of supercoiling itself. This DAPI staining method will have wide possible application in the study of DNA and chromatin.