A batch of lyophilised human diploid-cell-strain rabies vaccine was divided into three batches, which were exposed to different temperatures during their distribution to and storage at three centres in Pakistan. Vaccine potency after exposure to these temperatures was tested by measuring antibody response in those given the vaccine, and by three different laboratory tests. The results indicate that the vaccine retains its antigenicity for man and for laboratory tests despite continuous exposure to high ambient temperatures for up to 11 weeks. These findings, together with current developments in vaccine manufacture and treatment schedules, offer considerable hope to many countries with low budgets for health care and where rabies is poorly controlled.