We show that for a linear space of operators M ⊆ B(H 1 , H 2 ) the following assertions are equivalent. (i) M is reflexive in the sense of Loginov-Shulman. (ii) There exists an order-preserving map Ψ = (ψ 1 , ψ 2 ) on a bilattice Bil(M) of subspaces determined by M, with P ≤ ψ 1 (P, Q) and Q ≤ ψ 2 (P, Q), for any pair (P, Q) ∈ Bil(M), and such that an operator T ∈ B(H 1 , H 2 ) lies in M if and only if ψ 2 (P, Q)T ψ 1 (P, Q) = 0 for all (P, Q) ∈ Bil(M). This extends to reflexive spaces the Erdos-Power type characterization of weakly closed bimodules over a nest algebra. 2010 Mathematics Subject Classification. Primary 47A15.