1.1. Very few of the languages of the Tai family still preserve consonant clusters of the type pl-, kl-, pr-, kr-, etc. The two languages generally known to preserve such clusters, at least in part, are Siamese and Ahom, the latter an extinct language of Assam.' The dialects of Wu-ming and Lung-an, both in central Kwangsi province,2 are the other dialects I know which preserve them to a certain extent. The widely scattered distribution of these languages shows that the preservation of the clusters indicates no specially close linguistic relationship among them. Three other languages-Lao,3 a language closely related to Siamese; Shan,' closely related to Ahom; and Dioi of Kweichow province,5 with which Wu-ming shares many common characteristics-have all simplified such clusters. It is safe to assume that the simplification is in most cases an individual dialect development, and that the clusters persisted in each of the various dialect groups before their simplification took place. 1.2. Since we are limited in this study to clusters of consonant plus liquid, the problem is to determine the various existing combinations. This task is complicated by two factors. (1) The first consonant is often modified by the following liquid, so that the modem forms often show altogether different articulations; cf. Siam. plaa 'fish' but T'ien-chow 6aa,6 Siam. took 'strips of bamboo' but Lungchow phjook.7 (2) There are two liquids, I and r, in Proto-Tai (abbr. PT), which are often redistributed in the dialects according to special conditions. Thus, Ahom has 1 after unaspirated initial consonants and r after aspirated initial consonants; Wu-ming has 1 in clusters, but r alone. Siamese is the only language where various contrasts are possible (pl-, pr-, phl-, phr-, etc.); but even there, as the comparative evidence shows, many clusters have been simplified, and some combinations (pr-, tr-, etc.) are hardly found to have correspondences in any other language except Lao. These forms may be either proven or suspected