Predictions lead to a lower interactome mapping cost for two reasons. First, predicted protein pairs are much more likely than arbitrary pairs to be true. Second, protein pairs with high prior probabilities do not require repeated positive measurements to confirm them as true interactions. Both effects underlie the finding that 450 new predicted interactions could be added to the interaction map using just 47 microtiter plates. In contrast, the Pooling strategy would require nearly 105 plates to add this number of interactions to the map.