Bifidobacterium and lactic acid bacteria (LAB), especially from the genera Lactobacillus and Lactococcus, are commonly used in the production of fermented dairy products due to their potential probiotic characteristics. Moreover, some strains of these microorganisms also have the ability to produce conjugated linoleic acid (CLA) from linoleic acid (LA), which has attracted much attention as a novel type of beneficial functional fermented milk. In the present work 22 probiotic bacteria were tested for the production of CLA, using a UV screening method and HPLC techniques. Five microorganisms, two strains of the genera Bifidobacterium, two Lactobacillus and one Lactococcus were selected for their ability to produce CLA after incubation in skim milk with free LA as a substrate. It was possible to quantify the production of CLA (in the range of 40–50μgCLA/ml) and identify the CLA isomers produced as C18:2 cis 9, trans 11 (60–65%), C18:2 trans 10, cis 12 (30–32%), C18:2 trans 9, trans 11 and C18:2 trans 10, trans 12 (2–5%).