The interactions between infections, malnutrition and poor iron nutritional status in infants at weaning ages are poorly defined. Therefore, four groups of infants from an area with a high incidence of malnutrition (Lahore, Pakistan) were enrolled in a prospective, randomized nutritional intervention study. Between 122 and 365 days of age, the infants from one community received either a milk cereal without iron fortification (n = 29), a milk cereal fortified with ferrous fumarate (7.5 mg/100 g; n = 30), or a milk cereal fortified with ferric-pyrophosphate (7.5 mg/100 g; n = 27). Forty-four infants from a neighbouring community did not receive a nutritional supplement and served as the control group. Calculated mean daily energy- and protein intake with the cereals was between 259-287 kcal, and 9.6-10.6 g at 12 months of age, respectively. Mean daily iron intake with the fortified cereals was between 4.1-5.1 mg at corresponding age. Nutritional supplementation resulted in significantly lower incidence of malnutrition and higher weight gain. Incidence of acute diarrhoea was significantly (p less than 0.05) lower in the supplemented groups. The infants fed the iron-fortified milk cereals had significantly higher hemoglobin (mean 10.4 vs. 9.8 g.dl-1) and serum ferritin (mean 13.3 vs. 8.5 ng.ml-1) values than the infants fed the non-fortified milk cereals. However, no differences in the incidence of infections were found between the supplemented groups. It is concluded that poor nutritional intake between 122 and 365 days of age substantially contributed to the high incidence of diarrhoea and malnutrition in Pakistani infants.