A new EC Regulation is being considered that may prohibit the continued use of CFCs for maintaining existing refrigeration systems and the use of HCFCs in new systems. This paper outlines the options for replacing CFCs and HCFCs in building air-conditioning systems, and reports recent findings from BRE work to investigate the performance of systems converted to an alternative refrigerant. This paper will be of interest to building owners and operators, architects, and building services engineers and consultants.