The objective of the project is to develop and test an intervention to promote exclusive breastfeeding (EBF), to assess its impact on infant health in African contexts where a high prevalence of HIV is a barrier and to strengthen the evidence base regarding the optimal duration for EBF. Promotion of EBF is the most effective child health intervention currently feasible for implementation at population level in low-income countries. It can lower infant mortality by 13%, and by an additional 2% were it not for the fact that breastfeeding transmits HIV. Only recently proven to be possible in hot and even dry climates, EBF without even offering water is still little appreciated by mothers or supported by health workers. EBF rates are especially low in Africa but the potential for rapid implementation may be high. A few studies elsewhere suggest that peer counselling can often achieve dramatic increases. Thus we propose to run the first randomised trial to develop and test models for applying this approach in four African countries and to quantify health benefits, cost-effectiveness and implications for the health care system. While experts realize that the HIV threat ought not to present much of a biological constraint to promoting EBF, in heavily affected countries it does represent a cultural constraint. Overcoming this will require the development of a safe and effective means of promoting EBF that is HIV-sensitive by taking into account the need to minimise postnatal HIV transmission. Thus, this study is linked to another (funded from elsewhere) to improve methods for doing so. Another scientific constraint to the promotion of exclusive breastfeeding for six months, as recommended by WHO, is uncertainty about its impact on the micronutrient status of infants. In a substudy, we will carefully follow markers of infant micronutrient status to see how they vary by feeding pattern, including EBF, for a longer period than has been examined previously.