In 1967 and 1968 Oleniacz and co-workers described an automated method enabling detection of low concentrations of different micro organisms by means of luminol. The method is based on the fact that; luminol, 5-amino-2.3-dihydro-1.4-phtalazindione, in the presence of iron containing organic and biological compounds give rise to chemiluminescence which is measured. The luminol method was adapted for use with a commercial autoanalyzer system. Coli bacteria from 3-8 different cultures were used for evaluation of the method. The number of bacteria were determined separately by viable counts. Standard error of the mean within the range of 10**4-10**7 bacteria per ml is +- 10 %. The method is extremely sensitive: Coli bacteria in water can be determined in concentrations as low as 10**4 per ml. The light emission is linearly dependent on the bacterial concentration over the investigated range of 10**4-10**7 bacteria per ml. Possible practical applications of the method are discussed.