Commercial DT fusion reactors need a breeding ratio (BR) of at least unity. The accuracy of BR calculations is limited by data uncertainties, especially the **7Li(n,n' alpha t) cross-section. A recent absolute measurement of this cross-section (4-14 Mev) is described. These results and other experimental evidence for a discrepancy in the ENDF/B evaluated cross-section are presented. The effect of the new measurements on various reactor blanket designs is also discussed.