As part of a long term air monitoring programme the ambient air in four UK urban areas was sampled throughout 1991. Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were sampled from the air in London, Cardiff, Manchester and Stevenage. Both vapour and particulate phases were collected at each site, and total concentrations are reported for 26 alternate weeks of the year. Total PAH concentrations (sum of 15 compounds) varied between 11 and 735 ng/m3 for the four sites. For each site PAH levels were dominated by the lower molecular weight compounds of phenanthrene, fluorene and pyrene, which made up more than 75% of the ΣPAH. The contribution of individual compounds to the total was broadly similar at each site in both the winter and summer. Concentrations of the higher molecular weight compounds were greater by a factor of 2.5 in the winter months. Eight PCB congeners (28, 52, 77, 101, 118, 138, 153 and 180) were measured at each site. London gave the highest recorded value of 3.85 ng ΣPCB/m3. Values at the four sites ranged between 0.19–3.85 ng/m3, this range being similar to levels reported in other European and American cities. Congeners 28 and 52 dominated the air mixture, comprising > 80% of the measured total. PCB concentrations in the summer were, on average, double those for the winter.