sign-changing solutions to semilinear elliptic problems inconnection with their Morse indices. To this end, we first establisha priori bounds for one-sign solutions. Secondly, usingabstract saddle point principles we find large augmented Morseindex solutions. In this part, extensive use is made of criticalgroups, Morse index arguments, Lyapunov-Schmidt reduction, andLeray-Schauder degree. Finally, we provide conditions under whichthese solutions necessarily change sign and we comment about furtherqualitative properties.