The vowel quality in some diphthongs of Swabian (a dialect of German) was determined by measurement of first and second formant values. A minimal contrast could be shown between two different diphthong qualities /(ae ligature)e/ and /(backward eh)i/, where for standard German only one is assumed, viz., /ai/. The two diphthong qualities differ only slightly in onset and offset vowel quality, so a better understanding of their relation was expected from an examination of the diphthong dynamics. Formant values (first and second formant) were taken at eight equidistant points during the diphthongs. The results suggest that there is a significant difference in the temporal patterns of the two diphthongs. Where /(ae ligature)e/ could be broadly described by a steady state onset to glide pattern, the other one is more adequately characterized as a glide to steady-state offset pattern. This dynamic aspect seems to be a very important field in need of further investigation into other diphthong pairs in Swabian, as in other languages.