Scientific experiments with non-human primates are viewed very controversially. Those who use non-human primates for scientific purposes contend that the results will be of great benefit to humans. They say that the distress to the animals is minimal and that, therefore, their experiments are ethically acceptable. On the other hand, there are those who oppose non-human primate experiments altogether, due to the close relationship between these animals and humans. In a literature study on non-human primate experiments in fundamental brain research, the outcome of research projects performed over the period of a decade was evaluated retrospectively. Objective criteria were applied both for determining the cost (internationally published distress scores, taking into account distress due to procurement, transportation and housing) and the benefit (evaluating publications that arose from the experiments, citation scores and so forth). Taking the example of electrophysiological recordings in the brain of the awake macaque, this balancing ended up very different from that proposed by the scientists, and did not support the conclusion that the experiments had been ethically acceptable.