The inadequacy in seismic response of existing r.c. buildings designed for gravity only, as typically found in Italy before the introduction of seismic-oriented design codes in the 70’s, is herein investigated. The results of quasi-static experimental tests on beam-column joint subassemblies and on a three story frame system, performed at the Laboratory of the Department of Structural Mechanics of the University of Pavia as a part of a co-ordinated national project, are presented and discussed. The significant vulnerability of the joint panel zone region and the critical role of slippage phenomena due to the use of smooth bars and of inadequate anchorage were observed. Particularly brittle failure mechanisms due to the interaction of shear damage and stress concentration at the hook anchorage location occurred in the exterior joints. An overview of the structural response, of the hysteretic behavior and of the observed damage is given. Inadequacies of available analytical models in predicting local and global mechanisms are discussed.