The kinetics of tin-lithium exchange in heterocyclic alpha-aminoorganostannanes have been studied using Sn-119 rapid-injection NMR. By comparison of the observed relative rate constants, the effects of ring size, configuration, and conformation can be discerned. Stannylpyrrolidines transmetalate extremely rapidly, whereas the rate of transmetalation of stannylpiperidines varies from negligible transmetalation to rapid transmetalation. The evidence suggests that only one conformation of N-methyl-2-(tributylstannyl)piperidine transmetalates. N-Boc stannyl piperidines transmetalate at rates that vary somewhat, due in part to conformational effects.