Abstract. The classic problem of regularity of boundary points for higherorder partial differential equations (PDEs) is concerned. For second-order elliptic and parabolic equations, this study was completed by Wiener's (J. Math. Phys. Mass. Inst. Tech. 3:127-146, 1924) and Petrovskii's (Math. Ann. 109:424-444, 1934) criteria, and was extended to more general equations including quasilinear ones. Since the 1960-1970s, the main success was achieved for 2mth-order elliptic PDEs; e.g., by Kondrat'ev and Maz'ya. However, the higher-order parabolic ones, with infinitely oscillatory kernels, were not studied in such details. As a basic model, explaining typical difficulties of regularity issues, the 1D bi-harmonic equation in a domain shrinking to the origin (0, 0) is concentrated upon:where R(t) > 0 is a smooth function on [−1, 0) and R(t) → 0 + as t → 0 − . The zero Dirichlet conditions on the lateral boundary of Q0 and bounded initial data are posed:The boundary point (0, 0) is then regular (in Wiener's sense) if u(0, 0 − ) = 0 for any data u0, and is irregular otherwise. The proposed asymptotic blow-up approach shows that:(i) for the backward fundamental parabolae with R(t) = l(−t) 1/4 , the regularity of its vertex (0, 0) depends on the constant l > 0: e.g., l = 4 is regular, while l = 5 is not; (ii) for R(t) = (−t) 1/4 ϕ(− ln(−t)) with ϕ(τ ) → +∞ as τ → +∞, regularity/irregularity of (0, 0) can be expressed in terms of an integral Petrovskii-like (Osgood-Dini) criterion. E.g., after a special "oscillatory cut-off" of the boundary, the functioñ , a = constant ∈ (0, 3·23 ), together with typical ideas of boundary layers and blow-up matching analysis. Extensions to 2mth-order poly-harmonic equations in R N and other PDEs are discussed, and a partial survey on regularity/irregularity issues is presented.