Hollow-core floor slabs are the dominant flooring systems used in New Zealand since the 1980's. This study experimentally investigates the seismic performance of precast hollow-core floors including three-dimensional effects of an entire floor system within a two-way moment resisting frame. In order to experimentally assess the seismic perfo1mance of a large super-assemblage a new type of self-equilibrating loading frame was designed and built. A full-scale super-assemblage based on a multi-storey prototype was constructed and tested under quasi-static cyclic loading. The capacity designed precast concrete frame perf01med very well but the performance of the floor itself was quite poor. Incipient failure of the precast floor occurred at an interstorey drift of 1.9 percent, while complete collapse of the floor occurred at a drift of 2.5 percent. A rainflow counting method is developed to enable the amount of beam elongation to be predicted during an earthquake. This is particularly impmiant in determining the required seating length for the precast hollow-core flooring units. Based on the results of this investigation new connection (seating) details are proposed for attaching the hollow-core units to the supporting beams to try to improve the performance of the hollow-core units.