Pinfish (Lagodon rhomboides) were fed cerium-144 labeled food to determine if movement of the label could be used to estimate food evacuation time. Radioactivity was retained by the fish until their gastrointestinal tracts were empty. Replicate measurements showed that individual fish may have significantly different evacuation rates. Cerium evacuation and serial slaughter methods provided similar estimates of evacuation time; for the same precision fewer fish are needed for the cerium method. From these experiments, it appears that144Ce can be used as a tag to measure food evacuation time.