C-DNA is the canonical double helix form related to B-DNA. It is obtained in air-dried DNA fibers prepared from various aqueous salts, most commonly LiCl. The possibility of its existence in solution is unclear. We study conformational changes induced in supercoiled circular DNA by increasing LiCl concentrations. The physical properties of supercoiling allowed us to quantify changes in helical twist directly from circular dichroism (CD) spectra and to track conformations of DNA minicircles using atomic force microscopy (AFM). Both CD and AFM provide strong qualitative evidence that DNA helical twist increases with increasing LiCL concentration without any sign of saturation. The maximum increase estimated for the concentration range up to 8 M LiCl corresponds to the onset of the B-to-C DNA transition, suggesting stability of C-DNA at concentrations slightly above this level.