The growth of mastitis pathogens (eight strains) and non-pathogenic bacteria (eight strains) was studied using microturbidometry. All bacteria grew well in whey originating from uninflamed quarters. However, the growth of bacteria which are not considered to be mastitis pathogens (Lactobacillus plantarum, Bacillus subtilis, Streptococcus lactis and Pseudomonas fluorescens) became suppressed by whey from mastitic quarters. On the contrary, the growth of Staphylococcus taureus and Escherichia coli was generally better in mastitic samples. Streptococcus agalactiae showed inconsistent results.