IN the course of experiments using young guinea pigs as test animals, it was found that erythromycin given orally or intraperitoneally caused the animals to look ill after two to three days, with ruffled fur, anorexia, disinclination to move and subnormal temperature, followed by death on the sixth to eighth day with emaciation and signs of diarrhœa. No obvious common cause of death could be found macroscopically or microscopically in sections of liver, spleen, kidney or lung, although occasionally liver necrosis and renal tubular degeneration were seen, accompanied by albuminuria, red cells and casts in the urine and slightly raised blood urea.