In economic experiments decisions often differ from game-theoretic predictions. Why are people generous in one-shot ultimatum games with strangers? Is there a benefit to generosity toward strangers? Research on the neural substrates of decisions suggests that some choices are hormone-dependent. By artificially stimulating subjects with neuroactive hormones, we can identify which hormones and which brain regions participate in the decision-making, to what degree and in what direction. Does one hormone make subjects generous and another stingy? In this paper, two laboratory experiments are described using the hormones oxytocin and arginine vasopressin to see if oxytocin may make subjects more generous and is arginine vasopressin may do the opposite, make people stingy. Since these hormones naturally release during the day in response to the environment, it makes sense to test what happens when they change.