The final state $$D_s + l + \bar v_l + \cdots $$ occurring inZ 0-decay is analyzed, and backgrounds to the decay chain $$(i) Z^0 \to B_s + \cdots ,(ii) B_s \to D_s + l + \bar v_l + \cdots $$ are estimated. A resonance description is used to model the dominant source of background, and a numerical study yields estimates for the background-to-signal ratio of several per cent as input parameters are varied.