The Sui people (in Chinese ∈ Shui meaning ‘water’) constitute the second largest components of the Kam-Sui language grouping whose population according to the 1990 census was 346,000. But the Sui language has an importance far beyond its size, as this language has figured prominently in the history of research about the entire Kam-Tai family. It was namely the landmark investigations of Sui by Professor Li Fang Kuei in the 1930s and 1940s that proved a connection between Thai and some language groups of China. The Tai peoples are now thought to have once lived in this general area of China before departing for SE Asia. One important discovery Li made during his work was that the Sui language had preserved an inventory of sounds relatively rich and archaic in comparison to Tai groups of SE Asia. For example, the voiceless nasals of Sui /P =n=/, are perhaps suggested in Thai spelling yet not pronounced voiceless today, but in Sui they are still truly voiceless nasals. For that reason lexical comparison with Sui is singularly helpful in understanding the nature of the parent from which it and the other Tai languages have sprung.