Abstract Since 1984 more than 600 human milk samples have been analyzed in our institute for PCDDs, PCDFs, PCBs and organochlorine pesticides (OCPs). All samples were collected on a voluntary basis from nursing mothers mostly living in North Rhine-Westphalia as a service to women who wished to know their levels. A statistical evaluation of all analytical data and the questionnaires filled out by the mothers reveals high correlations for some specific PCDD/PCDF and PCB congeners, respectively. The levels of these contaminants are mainly influenced by personal data, such as age of the mother, number of breastfed children and length of nursing period. On the other hand, the area of domocile, whether urban or rural, seems to have no effect on the body burden of these contaminants. In addition, there is some indication that certain living conditions, like an open chimney in the house and also particular consumption habits, such as lactoovovegetarian diet result in somewhat higher PCDD/PCDF levels in humans. Moreover, it is striking that mothers who are or have been active smokers for a longer time show lower PCDD/PCDF levels than non-smoking women. The same phenomenon can be noticed for mothers who are heavily influenced by smoking parents, companions or colleagues. Due to the ban of persistent, lipophilic pesticides in almost all countries of the Western World the levels of these compounds decreased permanently during the past ten years. A similar trend, even though somewhat less striking, is also apparent for PCBs and PCDDs/PCDFs over the past two years.