Many EPG studies have focused on alveolar and velar plosives and fricatives; however, few studies attempted to investigate bilabial articulation. It is not clear what the lingual pattern occurs when lingual contact is least expected during the bilabial production. Seven English-speaking subjects took part in an experiment to produce /p/, /b/ and /m/ in 6 intervocalic contexts --- i-i, i-u, i-a, u-u, u-i, u-a. The preliminary results indicated that EPG contact decreased in both i-i and u-u vowel contexts. When the three test segments – /p/, /b/ and /m/ occurred in the remaining four asymmetrical vowel contexts, fewer EPG contact was observed in the i-a context than that in the i-u context. A similar pattern of the decrease in EPG contact was also found in the u-a context as compared to that in the i-u context. These results suggested that the adjacent vowels affected the observed degree of EPG contact during the bilabial production. These findings will be discussed in terms of anticipatory assimilation.