['To evaluate the impact of promotion of exclusive breastfeeding on infant health in Guinea-Bissau, West Africa, where mortality rates are high, breastfeeding is widely practiced but exclusive breastfeeding is rare.', 'At the Bandim Health Project in Guinea Bissau, West Africa, a birth cohort of 1721 infants were randomized to receive health education: promotion of exclusive breastfeeding for the first 4-6 months of life according to WHO recommendations at the time of the study. All children were followed from birth to 6 months of age.', 'Introduction of both water and weaning food was significantly delayed in the intervention group. However we found no beneficial health effects of the intervention; there was no reduction in mortality in the intervention group compared with the control group (mortality rate ratio: 1.86 (0.79-4.39)), weight at 4-6 months of age was significantly lower in the intervention group (7.10 kg vs. 7.25 kg; Wilcoxon two-sample test: p=0.03). There was no difference in diarrhoea morbidity and hospitalization rates.'] Is promotion of exclusive breastfeeding likely to be cost effective in West Africa . A randomized intervention study from Guinea-Bissau?