L-[U-¹⁴C]-2, 3-diaminopropionate was metabolised slowly in the rat. Nearly 75% of the total radioactivity could be accounted for by respiratory CO2 (60%) and by the concentration of the isotope in the liver and kidney (15%). The rate limiting step in its metabolism may be the activity of 2, 3-diaminopropionate: ammonia lyase in the liver. It is more readily metabolised than its 3-oxalyl derivative, which is neurotoxic.