The data here are from Lao spoken by majority groups and minority groups in contact with the other Lao dialects. When Lao dialects have long been in contact with each other, it is worthwhile to investigate whether tone variation and change have occurred. 

Gedney?s concept of the tone box is adopted. The tone data are analyzed auditorily and acoustically. The typical distinctive tonal patterns of the Lao language are proposed. To determine how these distinctive tone have been preserved in Lao dialect in contact, they were then compare to the ones in the Lao dialects in this study. The tonal systems of the Lao dialects are also compared to the ones in the available literature in order to find explanations for language variation. 

The findings here reveal tonal variations and changes in both majority and minority Lao induced by both internal and external factors. The tonal system of some Lao dialects differ from the patterns expected to have been derived from the typical distinctive tonal patterns. Pronunciation borrowing is hypothesized as one of the important factors leading to variation and change. The pattern of tonal mergers and splits, as well as tonal characteristics, found here to be different from those in the literature, lead to the supposition of language contact change. The results are also helpful for identifying ethnic groups.