This paper evaluates, in terms of speech signal processing, a non- linear method of pitch detection based on the detection of the zero- crossings of the signals (ZC method), in adverse conditions of interference. First, F0 identification is evaluated according to the relative level of energy between the components in mixtures of pure tones or pairs of vowels; then, we introduce in the double-vowel paradigm a confidence measure based on the standard deviation of inter-zero intervals. Finally, the robustness of this confidence measure is tested in two cases of interference : pure tones + noise, and vowels + noise. We show that the method allows to detect periodicity without any knowledge about the nature of the interfering sources, and then to identify their fundamental frequency.