Pentachlorophenol (PCP), used as a wood preservative and as a disinfectant, has been found in human urine samples from Saskatchewan and in air samples from three Canadian sites. To confirm the presence of atmospheric PCP residues and to explore seasonality, weekly samples were collected at five Canadian sites for three consecutive weeks, in the months of July and October, 1995 and January, April and May, 1996, using a high volume sampler equipped with polyurethane foam (PUF) plugs. PCP was present in all samples collected adjacent to a utility pole storage site with concentrations ranging from 0.7 to 1233.0 ng m-3. There was a very strong correlation between average weekly air temperature, measured over a range of -29.3 to +20.0 degrees C, and the log10 of the average weekly concentration of PCP at this site. PCP was measured in 7 of 11 air samples from each of two small cities (concentrations ranging from 0.2 to 6.8 ng m-3) and the correlation between temperature and PCP concentration, for these two city sites, was similar to that for the utility pole storage site. Concentrations of PCP at two rural sites were lower (0.1-1.5 ng m-3) and detected less frequently. As a consequence, the correlation between air temperature and PCP concentration was more variable.