Rhodococcus chlorophenolicus PCP-1, a mineralizer of polychlorinated phenols, was inoculated into natural sandy loam and peaty soils with pentachlorophenol (PCP) at concentrations usually found at lightly and heavily polluted industrial sites (30 to 600 mg PCP/kg). A single inoculum of 10(5) to 10(8) cells per g of peat soil and as little as 500 cells/g sandy soil initiated mineralization of(14)C-PCP. The mineralization rates of PCP were 130 to 250 mg mineralized per kg soil in 4 months in the heavily (600 mg/kg) polluted soils and 13 to 18 mg/kg in the lightly (30 mg/kg) polluted soils. There were no detectable PCP mineralizing organisms in the soils prior to inoculation, and also there was no significant adaptation of the indigenous microbial population to degrade PCP during 4 months observation in the uninoculated soils. The inoculum-induced mineralization continued for longer than 4 months after a single inoculation. Uninoculated, lightly polluted soils (30 mg PCP/kg) also showed loss of PCP, but some of this reappeared as pentachloroanisol and other organic chlorine compounds (EOX). Such products did not accumulate in theR. chlorophenolicus-inoculated soils, where instead EOX was mineralized 90 to 98%.R. chlorophenolicus mineralized PCP unhindered by the substrate competition offered by the PCP-methylating bacteria indigenously occurring in the soils or by simultaneously inoculated O-methylatingR. rhodochrous.