Double electron electron resonance (DEER) is an EPR technique which allows for distance measurements on the nanometer scale. Here, EPR-based distance measurements were extended to in-cell applications. From evaluation of nitroxides for experiments in intracellular environment of Xenopus laevis oocytes and through proof-of-principle experiments optimal parameters for performing in-cell DEER were found. On the example of G-quadruplexes formed by oligomers of human telomeric DNA, DEER was shown to be applicable for structural identification of biological objects under their native conditions.