We show how subintegral extensions of certain local Noetherian domains S can be constructed with specified invariants including reduction number, Hilbert function, multiplicity and local cohomology. The construction behaves analytically like Nagata idealization but rather than a ring extension of S, it produces a subring R of S such that R ⊆ S is subintegral.Let i > 0, and choose 0 = c ∈ J i (J + I) ∩ C. By (2.4), the mapping g : R/cR → S/cS ⋆ K/cK induced by f is an isomorphism of rings. Therefore, from (3) we haveThus since g is an isomorphism, there is an isomorphism of A-modules:The second isomorphism is also an isomorphism of R-modules, where the R-module structure is the usual one on the direct sum. Indeed, since S = A + cS, we have R = A + cS ∩ R. Moreover, c ∈ J, and J = JS ∩ R, so R = A + cS ∩ R = A + J, and from this it follows that this isomorphism of A-modules is also an isomorphism of R-modules. This verifies (1). Now a similar argument using (4) and (5) instead of (3) shows that when I ⊆ J there is an isomorphism of R-modules for all i ≥ 0,and this verifies (2). Now to prove statement (1) of the theorem, we make use of the isomorphisms (1) and (2). We consider the case first where we make no assumption about whether I ⊆ J. Since S = R + JS, it follows that the lengths of the S/JS-modules, J i IS/J i+1 IS and J i−1 (I + J)K/J i (I + J)K, agree with their lengths as R/J-modules. Therefore, we have by (1) that for all n ≥ 1, H J,I (n) = length J n I/J n+1 I = length J n IS/J n+1 IS + length J n−1 (J + I)K/J n (J + I)K = H JS,IS (n) + H JS,(I+J)K (n − 1).