Bovine mastitis is one of the most frequent and economically important diseases in dairy cattle. In the case of the cumulative occurrence of clinical mastitis or of increased bulk milk somatic cell counts, an extensive analysis of problems can be the base for reasonable recommendations. The troubleshooting has to include the analysis of the machine milking process. During milking, the risk of new intramammary infections can increase. For an average dairy herd, the proportion of milking effects on new infection rates is estimated to be approx. 20%, whereas direct effects (transmission of mastitis-causing pathogens) may be responsible for half of new infections. Beside the contamination of teat tip and the teat canal orifice with pathogens, microorganisms can be transferred into the mammary gland by changes in the milking vacuum. In the present paper, the current knowledge is described in a practice-oriented way.