N-Nitrosoatrazine and N-Nitrosocarbaryl can be efficiently recovered from the whole mouse by use of a frozen animal procedure in combination with organic solvent extraction. Final qualitative and quantitative analysis is performed by high-performance liquid chromatography in combination with the TEA analyzer (HPLC-TEA). A recovery curve for N-nitrosoatrazine from Swiss CD1 mice indicates an unusually long half-life, especially when compared with more volatile N-nitroso derivatives. These results are of interest in regard to the possible in vivo formation of N-nitroso derivatives of agricultural chemicals.