The objective of this study was to determine the fate of a pulse-labeled oral dose of uniformly labeled [14C]taurine in cats fed four separate diets. The diets were a heat-processed commercial diet, the same diet frozen-preserved and two purified diets containing 0 or 1325 mg taurine/kg. The commercial formulations contained 1070 mg taurine/kg dry matter (by analysis). The excretion of 14C in CO2, urine and feces was monitored. Significant quantities of 14CO2 were produced, with greater amounts excreted by cats fed the heat-processed commercial diet (9.4% of initial dose) than by those fed the frozen-preserved diet (0.09%), indicating extensive taurine degradation by the intestinal microflora. Purified diet groups were intermediate between the two commercial diet groups. Carbon-14 excreted in urine peaked at 24 h and was highest for cats fed the frozen-preserved commercial diet or 1325 mg taurine/kg purified diet. Carbon-14 excreted in feces was highest for cats fed the two commercial diet formulations, with peak amounts at 48-72 h. Because the frozen-preserved commercial diet had previously been shown to maintain plasma taurine concentration, whereas the heat-processed diet did not, these results indicate that processing affects the digestive and/or absorptive process in a manner that increases the catabolism of taurine by gastrointestinal microorganisms.