SummaryChondroitin sulfate extracted from human costal cartilage was prepared in 3 different ways for inoculation into rabbits, (1) a 1% solution, (2) a 1% solution incubated with heat-killed, group A, type 3, hemolytic streptococcus, and (3) a 1% solution incubated with heat-killed Staphylococcus aureus. These 3 preparations were injected into rabbits in an attempt to elicit antibody production. There was no evidence of the formation of precipitating antibodies against chondroitin sulfate in any of the rabbits'sera nor was there any clear indication of the acquisition of skin sensitivity by any of the rabbits.