Let M be a closed,
connected, smooth and 2-connected mod2 (i.e., Hi(M,Z2) = 0,0 < i ≤ 2)
manifold of dimension n = 4k + 2 with k > 1. We obtain some necessary and
sufficient conditions for the span of an n-plane bundle η over M to be greater than or
equal to 4. For instance for k odd span M ≥ 4 if and only if χ(M) = 0. Some
applications to immersion are given. In particular if n = 2 + 2l, l ≥ 3 and
w4(M) = 0 then M immerses in R2n−4.