A range of bait materials (kangaroo and horse meat, beff, crackle, egg and oats) was used during pest control programmes that utilized sodium monofluoroacetate (1080 poison). These materials were assayed for the presence of microorganisms (fungi and bacteria) and the ability of these microorganisms to defluorinate 1080 was investigated. In general, the defluorinating activity was low when 1080 was the sole carbon source, but in the presence of an alternative carbon source (e.g. peptone-meat extract) the defluorinating ability of many organisms was greatly enhanced. The extent of defluorination varied among the different types of organisms associated with the baits. Microorganisms isolated from oats and kangaroo meat showed the highest defluorinating activity, whereas those associated with crackle and egg had the lowest. Of the isolates tested only Fusarium oxysporum exhibited high defluorinating ability in soil, defluorinating approx equal to 72% of the available 1080 (20mM) in 15 d at 27 deg C. The implications of these findings for predator/pest control are discussed.