Severe acute respiratory syndrome (SARS) and avian influenza are two important newly emerged infections with pandemic potential. Both infections have crossed the species barrier to infect humans. SARS originated from southern China and spread to many countries in early 2003. The close collaboration of scientists around the world resulted in a rapid identification of the causative agent, and the early isolation of infected cases and meticulous infection control measures were the key to successfully controlling the outbreak of SARS. The first outbreak of human cases of avian influenza was reported in 1997 in Hong Kong. Since 2003, there have been many small outbreaks of human cases around the world, and the reported mortality is greater than 50%. Current evidence suggests that the human-to-human transmission of avian influenza is rather inefficient, but mutation might occur in the future resulting in improved transmission and possibly a pandemic in humans. As with the outbreak of SARS, the development of sensitive and accurate early diagnostic tests is extremely important for successful control of the outbreak at source. The availability of isolation facilities, the stockpiling of antiviral agents and effective and safe vaccination will be extremely important in minimising the damage of a new influenza pandemic.