Mixed-function oxidase activity in a desert rodent, Notomys alexis.

1. The levels of enzymes associated with the hapatic mixed-function oxidase system, and the rates of oxidation of three substrates, are compared in the desert rodent, Notomys alexis, and the laboratory mouse, Mus musculus. 2. In general, the activity of the mixed-function oxidase system in Notomys alexis is greater than in Mus musculus. 3. Previous reports of the low rates of elimination of lipophilic compounds in the desert rodent are therefore not explicable by differences in metabolism. It is suggested that the lower rates of urine production is a more likely explanation. 4. The production of small volumes of concentrated urine is suggested to result in the longer retention of some foreign compounds.