Polynuclear aromatic hydrocarbon (PAH) data are presented from a long-term field experiment in which soil plots were amended with single additions of sewage sludges over 20 years ago. Five sludges, each containing a different concentration of PAHs and enriched with different heavy metals (Cu, Cr, Ni or Zn), were applied to five soil plots in 1968. This increased soil PAH concentrations substantially, but by 1972 some plots had lost up to 60% of the PAHs applied. By 1989, losses had increased to about 90%. Individual PAHs have behaved differently with compound persistence a function of molecular weight. Half-lives for the compounds in soil increased from < 2 years for naphthalene to > 16 years for coronene. It is argued that biological degradation is the most important loss mechanism for PAHs in this soil. Overall, calculated half-lives are significantly longer than those previously reported under experimental conditions. The implications of this are discussed. Slower PAH degradation was observed in the plot amended with the Ni-rich sludge; by 1989, 35% of the applied PAHs was still detectable in the soil. This may be indicative of long-term heavy metal interference in microbial processes.