The paper deals with the reflexes of Proto-Samoyedic *ä and *a in the first syllable. It shows that their reflexes in Nganasan correlate with the synharmonical class of the root: while in the former front-vowel roots *ä became e and *a became Ća or Cia, in the former back-vowel roots both have passed to Ca. This development is paralleled in Selkup, Kamas and Mator, while in Nenets and Enets both *ä and *a have each developed regardless of the synharmonical class