Normal and splenectomized rats were challenged with Streptococcus pneumoniae type 1 via different administration routes. In experiment I, previously splenectomized or sham—operated rats received 4 times 103 colony—forming units (CFU) of pneumococci via (i) a peripheral vein, (ii) subcutaneously, or (iii) intraperitoneally. The results indicated an increased susceptibility of the splenectomized animal to pneumococci administered via all three routes. However, subcutaneously administered pneumococci gave a lower mortality than pneumococci given intravenously or intraperitoneally. In experiment II 40 splenectomized rats received 4 times 103 CFU of pneumococci via (i) peripheral, (ii) portal, or (iii) caval veins or the aorta. No differences in mortality were found. In experiment III, non-operated animals received 4 times 105 CFU of pneumococci either intravenously or intraperitoneally, resulting in mortality rates of 0/20 and 17/20, respectively. After 2 weeks the rats surviving intravenous challenge received 4 times 105 CFU of pneumococci intraperitoneally; all survived. The data indicate the the spleen and the subcutis have a greater capacity to protect against pneumococci in the absence of specific antibody than the peritoneum or the circulation outside the spleen.