In a prospective study of 113 children in rural Bhutan, morbidity, nutritional status and feeding practices were recorded monthly over a period of 32 months. This information was related to seasonal variations in rainfall. Diarrhoea had a negative impact on growth, as measured in monthly intervals, during the second and third years of life, reducing daily weight gain by 4.4 +/- 2.0 g (p<0.0001). this impact was largest during the monsoon season. For respiratory tract infections the value was 2.6 +/- 1.7 g (p<0.01). Growth in weight was lowest during the monsoon period (p<0.0001). Continued breast feeding was associated with an odds ration for diarrhoea of 0.51 (95% CI 0.34-0.78), and for respiratory tract infections of 0.63 (95% CI 0.40, 0.99). Growth in weight was less reduced during the monsoon season for children who were breast fed (2.5 +/- 1.7 g/day) than for those not breast fed (7.5 +/- 3.5 g/day) (p<0.01). We conclude that breast feeding is of particular importance throughout the warm and rainy season.