The influence of creatinine, urea and guanidine injection on the course of an artifically induced inflammatory reaction has been studied in rats. The formalin and bolus alba edema served as inflammatory models. It was shown that the inflammatory reaction was not significantly altered by urea. By creatinine, however, the inflammation was diminished. If urea and creatinine were given together the course of the inflammatory reaction was not altered significantly, suggesting an inhibitory interrelation between these two substances. Guanidines showed the strongest inhibiting effect on inflammation. It is discussed that guanidines influence energy availability by inhibition of oxydative phosphorylation.