Controlled studies with baits containing the biomarkers iophenoxic acid or tetracycline were carried out to measure bait uptake by free-living badgers. The presence of these biomarkers was determined in badger plasma and dentition. The biomarkers were then incorporated into baits to quantify bait uptake by badgers in the field. Seven captive badgers were orally dosed with iophenoxic acid, which was subsequently measured in serial plasma samples for 18 weeks. Subsequently, field studies using baits marked with iophenoxic acid were carried out at selected setts in two study areas. In other experiments, five cage-trapped badgers were orally dosed with tetracycline and released. These badgers were subsequently re-trapped and the presence of tetracycline measured in sections of canine teeth. Field trials were also carried out using baits marked with tetracycline in four separate study areas. Badgers dosed with iophenoxic acid had elevated plasma iodine in comparison to a pre-dose baseline level. The elevations in plasma iodine could be detected throughout the sampling period. Field experiments using iophenoxic acid showed that c. 80% of wild badgers had ingested the marked bait. In addition, all five badgers dosed with tetracycline had tetracycline deposits in their canine teeth. Between 20% and 77.8% of badgers trapped in the tetracycline field trials were positive for uptake of the tetracycline-marked bait. Variation in the percentage of badgers marked was attributed to several factors including seasonal timing of bait deployment. Our results indicated that iophenoxic acid and tetracycline were effective biomarkers of bait uptake by badgers.