According to the signature whistle hypothesis, bottlenose dolphins Tursiops truncatus emit individually sequential stereotyped whistles, which may function to broadcast the whistler's identity and location. Such whistles have been found in other dolphin species repertories. 12 hours of sound recordings of tucuxi dolphins Sotalia fluviatilis from Sepetiba Bay were analysed with the aim to detect such signature whistles. All of the whistle sonograms in which contours were stereotyped and sequential were selected and classified in "Types'' by means of two different methods: Visual Observation (VO) and a quantitative method named Contour Similarity technique (CS). 202 whistle sequences were chosen and classified in 27 Types by means of the OV method. Although the individuality of the Types was not demonstrated, the possibility that they might really represent signature whistles is reinforced by the following factors: the majority of the Types were formed of whistle sequences quite close to each other; they were mainly emitted during feeding and travelling behaviours; and were in accord with the general species repertoire. The CS technique did not correlate with the VO method in the whistles classification and it does not seem to be useful for the S. fluviatilis repertoire. I also selected 19 whistles sequences formed from two simultaneous components which resemble a kind of vocal interaction between dolphins known in the literature as "duet''
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