Twenty nine anaerobically digested, lagoon dried sewage sludges were analysed for polynuclear aromatic hydrocarbons (PAHs). These sludges had been applied to the plots of a long term agricultural experiment from 1942 to 1961. The exact dates of sludge production and treatment are unknown, although they are likely to be 1-5 years prior to sludge application dates. The sludges had a mean ΣPAH (defined as the sum of the compounds measured) concentration of 50 mg/kg, with a range of 18-125 mg/kg. The most abundant compound was benzo[ghi]perylene with a mean concentration of 10 mg/kg. A trend is apparent in the ΣPAH content through time, increasing until 1948 to over 125 mg/kg, then decreasing to 29 mg/kg by 1961. These changes are tentatively attributed to changes in air quality and smoke emissions. The PAH content of contemporary sludges is also reviewed.