We report here the study of the transition of a B-form of d(CGCGCGCGCGCG) to the Z-form as a function of the ions strength of PBS buffer. We used circular dichroism (CD) spectroscopy. Decomposition CD spectra by linear superposition provides evidence for one or more intermediate states that are distinct from the Band Z-forms of DNA. Linear decomposition is performed according to the locally linearized model (LLM) modified by the explicit introduction of the weight function essentially present in any quadratic integral of the spectra.