A systematic study of F0 perturbation by voiceless consonants in Cantonese is carried out. Apart from a voiceless interval introduced, a production asymmetry is found: F0 contours are raised by prevocalic consonants but lowered by postvocalic consonants at the C-V and V-C transitions. Moreover, initial consonants are found to differ in the duration of the voiceless intervals they introduce. Based on the recent finding that F0 production is synchronized with the syllable, we demonstrate that such durational differences need to be taken into consideration before accurate measurement of F0 perturbations can be made.