Abstract. We present a variant of the AINV factorized sparse approximate inverse algorithm which is applicable to any symmetric positive definite matrix. The new preconditioner is breakdownfree and, when used in conjunction with the conjugate gradient method, results in a reliable solver for highly ill-conditioned linear systems. We also investigate an alternative approach to a stable approximate inverse algorithm, based on the idea of diagonally compensated reduction of matrix entries. The results of numerical tests on challenging linear systems arising from finite element modeling of elasticity and diffusion problems are presented.Key words. sparse linear systems, finite element matrices, preconditioned conjugate gradients, factorized sparse approximate inverses, incomplete conjugation, stabilized AINV, diagonally compensated reduction AMS subject classifications. Primary, 65F10, 65N22, 65F50; Secondary, 15A06 PII. S10648275993569001. Introduction. We consider the solution of sparse linear systems Ax = b, where A is a symmetric and positive definite (SPD) matrix, by the preconditioned conjugate gradient method. In the last few years there has been considerable interest in explicit preconditioning techniques based on directly approximating A −1 with a sparse matrix M ; see, e.g., [7] Although the main motivation for the development of sparse approximate inverse preconditioners comes from parallel processing, it is becoming clear that these techniques are also of interest because of their robustness. Sparse approximate inverses are often applicable to difficult problems where other preconditioners may break down [4]. For instance, incomplete factorization preconditioners, while widely popular and fairly robust, are not always reliable, in that the incomplete factorization process may