Oxidising and non-oxidising biocides are commonly used in an attempt to control biofouling in industrial water systems. Many of these programmes, however, fail due to the incorrect selection and application of these chemical compounds. Knowledge of the organisms to be eliminated and system hydraulics are important operational parameters in ensuring the successful application of chemical control programmes. A further complicating factor is the build up of bacterial resistance to many of these compounds. One way of limiting resistance is the alternation of oxidising and non-oxidising biocides at the correct miminum inhibitory concentration and using these in combination with surface active compounds to dislodge any biofilm. A variety of surface monitoring techniques are in use in order to monitor the success of biofouling control programmes. Unfortunately none of these techniques are ideal and results have to be considered very carefully.