Chlorophenols may be present in soils by land application of biocides or chlorophenol- and chloroguaiacol-containing sludges from pulp bleaching effluent treatment. Polychlorophenols like 2,4,5-trichlorophenol (2,4,5-TCP) are priority pollutants resistant to biodegradation. In this work, the mineralization (14CO2 evolution) of [U-14C-2,4,5]-TCP in soil not previously exposed to chloroorganics was studied. After 60 days of incubation, soil mineralized 15-45% of 2,4,5-TCP when it was exposed to 1, 10, or 100 ppm of this compound. Minimal half-lives for 2,4,5-TCP of 35-170 days were estimated. Less than 2% of mineralization was observed in soil exposed to 500 ppm or in incubations with sterile soil spiked with 10 or 100 ppm of 2,4,5-TCP. Thirty days of preincubation of soil with 10 or 100 ppm of 2,4,5-TCP increased the rate of mineralization of an additional amount of this pollutant. On the other hand, the presence of a mixture of chloroguaiacols decreased the mineralization of trichlorophenol in this soil. No microorganisms were able to grow using 2,4,5-TCP as the sole carbon and energy source. However, the absence of mineralization in sterile soil, the effect of the amount of and the preincubation with 2,4,5-TCP, and the effect of the presence of chloroguaiacols strongly support the involvement of microorganisms in this degradative process.