Following the method of Ashbaugh-Benguria in Comm. Math. Phys. 124 (1989), 403-415; J. Differential Equations 103 (1993), 205-219, we prove an upper estimate of the arbitrary eigenvalue ratio (mu(m)/mu(n)) for the regular Sturm-Liouville system. This upper estimate is sharp for Neumann boundary conditions. We also discuss the sign of mu(1) and include an elementary proof of a useful trigonometric inequality first given in the aforementioned articles.