A series of four adaptation experiments using Thai subjects is being carried out in order to investigate a possible phonetic contribution to adaptation effects on a voicing continuum. Thai subjects divide a VOT continuum into three phonological categories at the labial and dental places of articulation but only two phonological categories (voiceless inaspirates and voiceless aspirates) at the velar place. The effects of −70‐msec labial and velar adaptors on both a labial and a velar VOT continuum were determined. If there is a phonetic contribution to adaptation, a −70‐msec velar adaptor should produce a significant boundary shift between voiceless inaspirates and voiceless aspirates on both the velar and the labial VOT continua, while a −70‐msec labial adaptor will affect neither boundary. If, however, adaptation takes place solely at an acoustic level, both adaptors will shift the boundary between velar voiceless inaspirates and voiceless aspirates, but will not affect the boundary between labial voiceless inaspirates and voiceless aspirates. Preliminary results indicate the presence of a phonetic contribution to the adaptation effect. [Work supported by NICHD.]