Rats received different levels of threonine (Thr), one, 1.7 and four times the normal dietary intake, from conception to adulthood. The mothers were fed the experimental diets before and during pregnancy. Their offspring received a daily oral load of Thr or placebo until weaning. Thereafter, the juveniles were fed the same diet as their mothers. Morphologic development, ingestive behaviour, homing, and locomotion were observed before weaning. Exploration and spontaneous alternation were studied thereafter. Animals exposed during gestation to 1.7 times the normal Thr intake consumed more food during the test of independent ingestion. Grooming showed inconsistent variations between days 12 and 29 in pups fed 1.7 times the normal Thr intake. Rats performed equally well on the other behavioural tasks independently of the dietary treatment. We conclude that Thr intake as much as four times higher than the levels found in normal diets does not impair the behavioural ontogenesis of the rat.