Colonies of honey bees (Apis mellifera L.) were surveyed for the presence of the honey bee tracheal mite (Acarapis woodi Rennie) in Finland between 1991 and 1997. Colony background information and winter loss data were obtained from beekeepers who had taken tracheal mite infested samples. A total of 2116 samples from honey bee colonies of 402 beekeepers were investigated. Infestations were found in 8% of the beekeeping operations and in 10% of the samples inspected. In the last years of the survey more than 20% of apiaries were infested. This increase may be partly explained by tracheal mite infestations found in commercial queen-rearing apiaries. A field experiment with colonies infested at different levels showed that colonies in which 20% or more of bees are infested with tracheal mites have an increased risk of dying during the winter under Finnish conditions. This infestation level was found among colonies in 92% of the infested apiaries. Comparison of the tracheal mite prevalence in apiaries with their winter losses indicated that infestations were associated with colony mortality. The results of this survey point to the high pest potential of the tracheal mite in Finland, in contrast to findings on tracheal mites from elsewhere in Europe. Therefore, strategies to prevent further spread of the mite are highly recommended and methods for effective control should be sought.;