A comprehensive investigation of a number of aspects when using formamide as background electrolyte solvent in capillary zone electrophoresis was presented. It included (i) the change of the ion mobility with ionic strength, (ii) the influence of the ionic strength on diffusion coefficients, and (iii) on the separation efficiency expressed by the maximum reachable plate numbers (when only longitudinal diffusion contributed to zone broadening), (iv) the effect of the solvent on pK(a) values (taken from the literature) of neutral and cation acids, (v) the establishment of the a pH scale in formamide by dissolving acids with known pK(a) values and their salts at defined proportion (thus circumventing the problem of calibrating the pH meter), (vi) the agreement between the experimentally derived and the theoretical dependence of the effective mobility on pH, (vii) the uptake of water of this hygroscopic solvent from the humidity of the environment and its consequence to the ion mobilities, pK(a) values, and the chemical stability of the solvent (e.g., hydrolysis), and finally (viii) the use of conductivity and indirect UV absorption to enable detection of analytes below the optical cutoff of formamide.