In connected speech, the acoustic properties of Mandarin tones undergo modifications not observed in isolation. The current study investigated the perceptual distinction between Mandarin tones in connected speech, focusing on Tone 3 and Tone 4, which have been reported to share a similar initial falling contour. The current study also tested whether syllables produced with focus and / or in certain syllable positions affect the tonal perception. In a forced choice perception task, participants heard syllables extracted from three syllable words previously recorded in short dialogues, and were instructed to select one of four characters representing corresponding monosyllabic words differing only in tone. The accuracy results showed that Tone 4 was much more successfully identified than Tone 3. Nonetheless, after using a d-prime analysis to control for an observed T4 response bias, we found the same level of perceptibility of T3 and T4. Furthermore, the two tones were better perceived when a tone was produced in a focus context or at the edge of a word, confirming the effect of prosodic structure on tonal perception.