Toluene-induced cells of Pseudomonas putida NCIMB 11767 lost their ability to oxidise toluene within 300 h. under conditions of carbon/energy or nitrogen deprivation ar 30 degrees C, while incubation at 4 degrees C improved the stability of this activity. Provision of inducing substrates (toluene or phenol) to nitrogen-deprived cells at 30 degrees C also enhanced the stability of toluene oxidation, whereas provision of a non-inducing carbon/energy source (ethanol) led to a total loss of toluene oxidation within 160 h. Disappearance of toluene-induced proteins, at different rates accompanied the loss of toluene oxidation in carbon-deprived cells. The data suggest that degradation of one or more of the major proteins of toluene metabolism determines the stability of toluene oxidation in carbon-deprived cells, Around 40% of the whole-cell tolene oxidation rate was recoverable after cryopreservation (- 20 degrees C under glycerol) of toluene-induced cells but most of this recovered activity (86%) was associated with dead cells, These observations may have important implications for the application of these toluene-induced cells as in situ bioremediation catalysts.