The 209Bi shift and relaxation have been measured in several Bi-BiBr3 mixtures. The behaviour is very different from that observed in Bi-BiI3 mixtures. The 209Bi shift decreases strongly as BiBr3 is added to Bi and the relaxation rate increases rapidly. The NMR data give strong evidence for the formation of short-lived BiBr3 "molecules" in the metal rich mixtures.