INTRODUCTION: Effective immunisation programmes require a stable cold chain to maintain potency of vaccines from national stores through to delivery sites. AIM: To assess the effectiveness of the New Zealand cold chain and examine the possible impacts of policy changes over the same time period on cold chain effectiveness. METHODS: Heat- and freeze-sensitive monitors were attached to 5% of randomly selected childhood vaccines from 2002 to 2008. Six-monthly reports on data collected from monitor cards were collated and analysed to look for changes over time in freeze and heat exposure failures for vaccines. RESULTS: From December 2002 to June 2008 a total of 21 431 monitor cards were included in vaccines distributed from the national store; 9474 (44.2%) of all cards were returned and 8249 (38.5% of total) were correctly completed. Over this period the percentage of valid returns recorded as heat exposed decreased from 38% to 7% (?2 371, p< 0.0001); freeze failures decreased from 16% to 2% (?2 134.228, p< 0.0001), and overall wastage from 17% to 2% (?2 163.83, p<0.0001), giving estimated annual savings of nearly NZ$4 million. DISCUSSION: Significant improvements can be made in cold chain management with resulting savings in vaccine wastage. This study demonstrates that such improvements have been made in New Zealand in recent years. This is likely to be due to a combination of improving equipment, systems, education and training, increased provider attention and quality standards. KEYWORDS: Vaccination; cold chain; refrigeration; primary health care