THE elaboration by the soil organism Bacillus palustris of a depolymerase (D3) specific for the long-chained capsular polysaccharide of type III Diplococcus pneumoniae (SIII) (ref. 1) provides an opportunity to explore some of the mechanisms of immunological paralysis induced by SIII. The polymerase when incubated in vitro for prolonged periods with SIII cleaves it to hexasaccharides and smaller units2. It could readily be shown that when the products of this reaction are injected into adult mice they do not elicit an immune response. Thus, 5/5 mice injected with 0.5 ml. of a 21-h reaction mixture containing 40 µg SIII and 50 viscosity units of D3 failed to form antibodies. When these mice were later injected with 0.1 µg SIII they all formed antibodies against the SIII. When D3 is injected intravenously into mice which 12 h previously had received 100 µg SIII it rapidly clears the antigen from the circulation so that within 12 h SIII is no.sk>nger detectable by either the micro-precipitin or the complement fixation tests. The former test detects 0.1 µg and the latter 0.01 µg antigen. Although no a priori evidence existed it seemed just possible that the enzyme might even enter the cells containing the SIII and relieve the immunological paralysis caused by the injection of relatively large amounts of SIII.