  In a field-theoretical context, we consider the Euclidean $(\phi^4+\phi^6)_D$
model compactified in one of the spatial dimensions. We are able to determine
the dependence of the transition temperature ($T_{c}$)for a system described by
this model, confined between two parallel planes, as a function of the
distance($L$) separating them. We show that $T_{c}$ is a concave function of
$L^{-1}$. We determine a minimal separation below which the transition is
suppressed.
