Microbially influenced corrosion (MIC) makes an important contribution to corrosion in various industries. Considerable success has been achieved by the use of biocides. Little information for controlling MIC is, however, available on the effectivity of biocides against sulphate-reducing bacteria (SRB) due to the difficulties of culturing these organisms using conventional techniques. Conductance changes monitored using the Malthus system were evaluated as an alternative method of estimating numbers of Desulfovibrio desulfuricans for laboratory biocide evaluations. The correlation of log10 counts of Desulfovibrio cells in iron sulphite (IS)-medium using conventional techniques with detection times using the Malthus systems was highly significant (r=0,974), indicating that the Malthus system can be used as an alternative method to conventional media for the enumeration of SRB. Growth studies of Desulfovibrio using the Malthus system were useful in the evaluation of biocides. A 56% and a 100% kill was obtained when using 60 and 200mg/l quaternary ammonium compounds (QAC), respectively.