Abstract. Let B 0 (s, t) be a Brownian pillow with continuous sample paths, and let h, u : [0, 1] 2 → R be two measurable functions. In this paper we derive upper and lower bounds for the boundary non-crossing probability ψ(u; h) := P{B 0 (s, t) + h(s, t) ≤ u(s, t), ∀s, t ∈ [0, 1]}. Further we investigate the asymptotic behaviour of ψ(u; γh) with γ tending to ∞, and solve a related minimisation problem.