Abstract According to the traditional theory, the distinctive opposition which occurs in the Estonian words sada “hundred”-saada “send, impt.”- `saada “to get, receive, inf.”, lina “flax”-g. linna-p. `linna “town”, g. silma-p. ` silma “eye” represents the different grades of quantity or duration of phonemes /a/, /n/ and /l/, i. e. in Estonian the phonemes have three degrees of quantity or length: the first, second and third degree (henceforth denoted as I, II, III). This theory was for the first time put forward by O. W.Masing in 1824. 1 Besides the length of single phonemes one also speaks of the length of phoneme clusters: in the word forms g. seina-p. `seina “wall” the diphthong in the first form is medium long or in II, in the second form extra long or in III; in the forms g. silma-p. ` silma the consonant cluster /lm/ in the first form is in II, in the second form in III.