Three batches of senile guinea pigs were injected i.m. daily with 80 mg/kg, 50 mg/kg, or 30 mg/kg up to 10 weeks. With the dosage employed neurons of the central nervous system showed in all animals a significant reduction of lipofuscin pigment. A characteristic type of vacuolisation of the pigment is a preliminary sign of its reduction in size and quantity. Residuals of lipofuscin can be detected in astrocytes and in greater quantity in microglia cells and cells of the capillary wall. The dissolution of lipofuscin is not only found in the CNS but also in the myocardium and in the liver. In the latter organs the removal of pigment is carried out by phagocytes towards capillaries. The actual uptake of phagocytes is believed to occur by the process of exocytosis and pinocytosis. A destruction or an invasion of neurons by microglia has not been observed. Lipofuscin removal at a very small rate by microglia cells appears to occur normally in the ageing animal, but is greatly enhanced by centrophenoxin. Cessation of drug application does not stop the process of removal at once and the process continues as far as we can judge by our experiments for several weeks without further drug application. Even 30 mg/kg per day were found to be sufficient to initiate and sustain lipofuscin removal.