The saliva of sheep was shown to contain significant concentrations of uric acid (16 (SD 4.5) pmol/l) and allantoin (120 (SD 16.4) pmol/l), sufficient to recycle purine derivatives equivalent to about 0.10 of the normal urinary excretion. When allantoin was incubated in vitro in rumen fluid, it was degraded a t a rate sufficient to ensure complete destruction of recycled allantoin. In a series ...