  In this paper the consistency of the de Sitter invariant $\alpha $-vacua,
which have been introduced as simple tools to study the effects of
transplanckian physics, is investigated. In particular possible non
renormalization problems are discussed, as well as non standard properties of
Greens functions. We also discuss the non thermal properties of the $\alpha
$-vacua and the necessity of $\alpha$ to change. The conclusion is that non of
these problems necessarily exclude an application of the $\alpha $-vacua to
inflation.
