The root-to-leaf delivery rates of ABA and ZR by xylem sap wereexpressed as the product of their xylem cytokinin concentrationsand the delivery rates of xylem sap from the roots to the leaves.The root-to-leaf delivery rates of ABA and ZR by transpiration wereexpressed as the product of their xylem cytokinin concentrationsand their transpiration rates. The percentage recoveries of IAA, GA3,ABA and ZR, determined by adding known quantities of the stan-dard hormone to a split extract, were 79.2%, 78.6%, 80.2% and 83.0%,respectively. This indicated absence of nonspecific inhibitors in theextracts. The specificity and other possible nonspecific immunore-active interference of monoclonal antibodies used here have beenexamined previously by