Increased attention has focused in recent years on environmental exposures which may elevate risk of human breast cancer. Following a brief introduction to the topic, we present a summary of recent evidence regarding the role of chlorinated hydrocarbons (e.g. pesticides), occupational exposures (e.g. electromagnetic fields), dietary factors, and other hydrocarbons (e.g. tobacco). Next, we present suggestions for additional measurements which may help to clarify the contribution of environmental factors, including individual and ecologic level exposure histories, polymorphisms in carcinogen-metabolizing enzymes, and interactions among environmental exposures, breast tumor characteristics, and other risk factors for breast cancer. Finally, we discuss how a population-based approach may be used to integrate these sources of information and could provide new clues regarding the role of environmental influences in breast cancer.