For newborns and infants, human milk is the best form of nutrition. However, human milk can be a source of xenobiotics with adverse effect on infants' health, therefore the potential risks need to be considered, in this case for the nephrotoxic mycotoxin ochratoxin A (OTA).In this work sensitive new OTA-biomonitoring methods were developed, validated and applied to human samples of both adults and infants. These methods allow the analysis of OTA and its metabolites, mostly ochratoxin alpha, and their conjugates in blood plasma, urine and also breast milk. The results obtained provide new insights into the metabolic fate of OTA in human adults and infants with dietary exposure to this mycotoxin. Analysis of OTA in blood and breast milk of women revealed that a considerable fraction of OTA is transferred from blood to milk, and that the lactational transfer of OTA can vary during the breastfeeding period. OTA-exposure of infants with breast milk was comprehensively investigated and showed a good correlation with OTA concentrations in infants' urines. This new data confirms the bioavailability of OTA in infants, and supports OTA urine concentration as a reliable biomarker of exposure for infants. Finally, comparison of data for OTA concentrations in human milk from Chile and Germany revealed geographical differences in the contaminant levels, with a transiently higher OTA exposure of Chilean than German infants.These new results are discussed in the context of current information of OTA levels in breast milk in other countries, the existing regulations for mycotoxin contaminants in foods and tolerable daily intake values for OTA which have been set for adults.