529 SUBSTRUCTURING METHODS FOR PARABOLIC PROBLEMS M. Dryja, November 1990 Domain decomposition methods without overlapping for the approximation of parabolic problems are considered. Two kinds of methods are discussed. In the first method systems of algebraic equations resulting from the approximation on each time level are solved iteratively with a Neumann-Dirichlet preconditioner. The second method is direct and similar to certain iterative methods with a Neumann-Neumann preconditioner. An analysis of convergence of the methods is presented.