The addition of composted PAH-contaminated soil to PAH-contaminated soil spiked with C-14-labeled pyrene resulted in rapid mineralization of pyrene (more than 57% after 21 days compared with 3.40% in unamended soil). The addition of the humic acid fraction of the composted soil also increased the mineralization potential of the soil significantly, but to a lesser extent (37.5% mineralization after 106 days compared with 20.6% in unamended soil). Increasing the humic acid concentration increased mineralization up to a maximum of more than three times the unamended rate, after which the rate of pyrene mineralization decreased, possibly due to inhibitory pH or concentrations of salts. The amendment of PAH-contaminated soil with materials containing humic acids or humic acid extracts is suggested as a method of bioremediation.