The addition of plerixafor to G-CSF decreases the risk of failed stem cell collection, but at considerable extra cost. Using a logistic regression model based on 354 autologous mobilizations, we have identified a local minimum peripheral blood CD34 count at which the probability of a successful collection is 50%. This seems an appropriate CD34 count at which to add immediate salvage plerixafor. J. Clin. Apheresis 28:378–380, 2013. © 2013 Wiley Periodicals, Inc.