Abstract. This paper deals with the problem of speech waveform polarity. As the polarity of speech waveform can influence the performance of pitch marking algorithms (see Sec. 4), a simple method for the speech signal polarity determination is presented in the paper. We call this problem peak/valley decision making, i.e. making of decision whether pitch marks should be placed at peaks (local maxima) or at valleys (local minima) of a speech waveform. Besides, the proposed method can be utilized to check the polarity consistence of a speech corpus, which is important for the concatenation of speech units in speech synthesis. Key words: speech synthesis, pitch marks, automatic pitch marking, glottal closure instants (GCIs), corpus recording, speech signal polarity