The influence of an oligoantigenic diet on different dimensions of the behavior of 21 children diagnosed as having attention-deficit hyperactivity disorder (ADHD) was examined. Treatment effects were assessed with three subjective measures (two questionnaires and an interview) and three objective measures (two attention tests and actometer). The study was divided into three phases: baseline, diet and provocation, each lasting three weeks. A crossover design was used. A significant effect was found for the subjective measures, but not for the objective measures. The results are discussed in terms of possible types of effects, e. g. rater effects and environmental effects. It may be that the oligoantigenic diet influences only certain dimensions of hyperactivity.