Chlorobenzenes in 40 anaerobically digested, lagoon dried sewage sludges were analysed by a Soxhlet extraction, Florisil clean-up and capillary gas chromatography method. These sludges had been applied to the plots of a long-term agricultural experiment from 1942 to 1961. Before application, the sewage sludges had been stored in lagoons at a sludge disposal works for about 1–5 years. Although some of the chlorobenzenes may have been lost during this period, substantial fractions remained at the time of field application. The mean concentration of the sum of the chlorobenzenes in the sludges was 43.7 μg/kg, with a range of 7.90–219 μg/kg. The five priority pollutants, i.e. 1,4-dichlorobenzene, 1,3-dichlorobenzene, 1,2-dichlorobenzene, hexachlorobenzene and 1,2,4-trichlorobenzene, were the most abundant. The concentrations of chlorinated benzenes generally decreased with increased chlorine substitution, although hexachlorobenzene and pentachlorobenzene were present at relatively high concentrations. 1,4-Dichlorobenzene and hexachlorobenzene increased over the period 1942–1961 in the sludges, whilst the other compounds analysed increased only from 1954 onwards. The relationship between organic matter contents and chlorobenzene recoveries from the sewage sludges was tested by experiments and the results are discussed. The results from the archived sewage sludges provide an outline of the chlorobenzene content in the environment of the West London area over a period when no monitoring was undertaken. Levels in the archived sludges are generally much lower, by perhaps an order of magnitude, than for contemporary samples.