Pen-reared coyotes (Canis latrans) voluntarily ingested small tallow baits containing 10 or 15 mg of iophenoxic acid, 100-mg mirex, and 150-mg rhodamine B. One week after treatment with 10 and 15-mg iophenoxic acid, mean serum iodine was elevated from pretreatment levels of less than 5 µg/100 mL to 175 and 324 µg/100 mL, respectively. Serum iodine levels declined to about 25 µg/100 mL after four months, but were still fivefold higher than controls. Coyotes that ate baits containing 100-mg mirex averaged 0.34-ppm mirex in serum one week later levels declined to 0.15 ppm after four months. Serum samples obtained 2 and 24 h after death contained higher concentrations of iodine and mirex than samples obtained immediately before death. Although some back guard hairs of coyotes fed 150-mg rhodamine B showed distinct fluorescent bands, rhodamine B did not appear to provide a dependable mark because all guard hairs were not marked.