Trapping, handling, and marking methods were evaluated for wild nutria (Myocastor coypus) in agricultural areas in Louisiana and Texas. Treadle-operated box traps, set on rafts instead of land, increased retrap response and reduced mortality. A modified leg-hitch sling and the tailhold method were found best for simple handling, and a light-weight restraining device was developed for close examination. Sodium pentobarbital injected intrathoracically at 50-60 mg!kg was the safest and most consistent anesthetic; carrot baits treated with diazepam effectively tranquilized nutria for safe handling. Nutria showed gross physiological rejection of nearly all marking materials tested (coloring agents and such objects as tags, flags, pins, and collars attached to or through the skin of various parts of the body). A No.3 self-piercing monel metal animal tag inserted through a web in the hind foot was the only reliable, long-lasting marking method tested, but it was inconspicuous. Acceptable short-term markers included ear tags, a white reflective paint, and radiotransmitter collars.