ELA, Volume 4, pp. 39-47, October 1998, abstract. P^alpha-matrices and Lyapunov scalar stability Daniel Hershkowitz and Nira Mashal For partitions alpha of {1,...,n}, the classes of P^alpha-matrices are defined, unifying the classes of the real P-matrices and of the real positive definite matrices. Lyapunov scalar stability of matrices is defined and characterized, and it is shown also that every real Lyapunov alpha-scalar stable matrix is a P^alpha-matrix. Implication relations between Lyapunov scalar stability and H-stability are discussed.