Pseudomonas putida bearing the archetypal TOL plasmid pWW0 metabolizes p-methylbenzoate through a meta-cleavage pathway. In complex environments such as soils that are relatively rich in organic matter, we observed metabolism of p-methyl-14C-benzoate, which could be monitored as 14CO2 evolution from the labelled alkylaromatic. Linear 14CO2 evolution in soils took place for at least a month, although efficient mineralization of the alkylaromatic required appropriate mass transfer to allow the bacterial cell and target chemical to remain in close contact.