Excretion of radioactivity by mink (Mustela vison) during 7 days after intraperitoneal injection of two different amounts of aflatoxin B1 was studied. Male mink that received a single dose of 25 mug aflatoxin B1/kg body weight excreted an average of 89.5% of administered radioactivity (56.8% via feces, 32.7% via urine); whereas female mink excreted an average of 85% (63.6% via feces, 21.4% via urine) of administered radioactivity during the 7-day period. Male and female mink given 150 mug aflatoxin B1/kg body weight excreted an average of 76.9-80.1% of administered radioactivity during the 7 days that followed treatment with toxin. These mink excreted somewhat more of the administered radioactivity in their urine than did the mink that received the lower dose of aflatoxin (37.2 vs. 32.7% for males and 32.7 vs. 21.4% for females). Regardless of sex and dosage of toxin, most of the radioactivity ultimately excreted either through feces or urine appeared in the first 24 h after toxin was administered to mink.