With assistance from WHO the Hungarian Ministry of Health organized two cold chain studies: the first in three counties in summer (1 July to 30 September 1987), the second in six counties (including the previous three) in winter (1 January to 31 March 1988). The counties were chosen according to their distance (50-300 km) from Budapest, individual districts and child health centres being selected randomly. All participants were trained before beginning the studies. The vaccines (DPT, measles and BCG) for immunization, with attached cold chain monitors, were transported from the manufacturers to the child health centres using the normal distribution systems in the country. The whole cold chain process was analysed with regard to (1) actual exposures to adverse temperatures and delays in distribution; (2) the places where such exposure or delay occurred; (3) the percentage of vaccines at risk of deterioration (actual and predicted) at the end of the study; and (4) the performance of refrigerators of different types. Evaluation of the results (using WHO's EPIC software) showed significant deviations from acceptable standards. This first cold chain study in a European country proves that even in a temperate climate and with a reasonably well-organized public health service there can be significant weaknesses in the transportation and storage of vaccines. Recommendations to overcome these deficiencies are given.