In this paper, we study the existence and non-existence of maximizers for the Moser-Trudinger type inequalities in R N of the formHereαN ] and ΦN (t) := e t − N−2 j=0 t j j! where αN := N ω 1/(N−1) N−1 and ωN−1 denotes the surface area of the unit ball in R N . We show the existence of the threshold α * = α * (a, b, N ) ∈ [0, αN ] such that DN,α(a, b) is not attained if α ∈ (0, α * ) and is attained if α ∈ (α * , αN ). We also provide the conditions on (a, b) in order that the inequality α * < αN holds.2010 Mathematics Subject Classification. 47J30; 46E35; 26D10.