A mixed microbial culture was entrapped into porous silica gel prepared by two different sol-gel methods. The immobilization of cells into prepolymerized tetraethoxysilane was more stressful to living microbial cells than the entrapment into colloidal SiO2. Our experimental equipment operating in a sensor mode was able to detect 0.5 mg phenol l(-1) and had a linear response in the range from 2 to 10 mg phenol l(-1).