A constitutive blocked mutant (UV4) of Pseudomonas putida was grown in a 2.5-1 fermenter on a mineral salts medium. Glucose was fed normally over an 18-h period. Gluconate reached about 5 gl(-1) in the medium and then fell to zero as it was utilised. The maximum toluene dioxygenase specific activity (2 gg(-1) h(-1)) was obtained over the last 6 h of the fermentation when the pH was fully controlled. In fermentations done at low dissolved O-2 tension (DOT) values there was an overall reduction in the cellular enzyme level. When stored at 4 degrees C in phosphate buffer, pH 7.0, harvested bacteria lost half their activity in about 90 h.