Humans bioaccumulate organochlorine pesticides throughout their lifetime due to the global environmental presence and physiochemical properties of these compounds, however, monitoring the current and lifetime exposure of the population to these compounds is complex. The collection and analysis of questionnaire data from Indonesia, human milk samples from Indonesian and UK born mothers living in Indonesia and milk samples during a 9-month lactation period as described in this thesis significantly contributes to the knowledge of human exposure to organochlorine pesticides and residue levels in human milk. Residue levels in milk samples from Indonesian mothers were positively correlated with the mother's age and parity, were higher in samples from urban than rural areas and did not show consistent correlations with diet. Correlations between pesticide levels and duration of lactation were not identified in a series of samples from the same mother or in samples from Indonesia. On a global scale residue levels from Indonesian samples were low, but p,p'-DDT was detectable in all samples and levels of y-HCH and p,p'-DDD were amongst the highest reported. The results from Indonesia including UK born women living in Indonesia coupled with existing data confirmed that the environment of Indonesia is contaminated with organochlorine pesticides and individuals had higher exposures in Indonesia than the UK. However, residue levels in milk samples from Indonesian women did not reflect the very high levels previously reported in local foods. An investigation into trends of organochiorine residue levels in human milk, foods and diets revealed that the consumption of animal fat significantly influenced human exposure and corresponding levels in human milk. Due to the extremely low consumption of animal fats by Indonesian people, the organochlorine levels detected in human milk did not reflect the environmental levels of these compounds. An exposure assessment model for residential Propoxur use in Indonesia was developed. It revealed that despite daily exposures, only low levels of Propoxur were likely to be absorbed and Propoxur exposure was unlikely to have toxicological effects. Despite more than 50 years of research, the detrimental effects of organochiorine pesticides in human milk have not been identified. The results indicated that 28% of Indonesian infants exceeded the acceptable daily intake (ADI) for Dieldrin, 90% exceeded the acute reference dose for total DDT and 24% for Endosulfan.