A long-term N balance study was carried out in five preschool children 3-4 years of age fed a cereal-legume-milk diet providing 1.75 g protein and 100 kcal (418 kJ) energy/kg body weight. This level of protein was found to be safe for preschool children in an earlier short-term N balance study. Continuous N balance was determined for 70 d in three subjects and 45 d in two subjects. All the subjects were found to be in steady positive N balance throughout the experimental period, the mean daily N retention varying between 54.5 and 87.5 mg/d. All the children increased their body weight steadily over the experimental period. No tendency of N balance to decrease with time was observed. It is concluded that the safe level of protein for preschool children estimated from a short-term N balance study is quite adequate when tested by a long-term feeding trial.