Summary: The proteic-polysaccharidic fraction KS-1A isolated from kapok seed by the same procedure as used to isolate CS-1A from cottonseed was shown to be a preformed, native protein. Three antigens common to cottonseed and kapok seed have been demonstrated by the Schultz-Dale technic. Fraction KS-1A was shown to contain a small amount of antigen which reacted like and is probably identical with CS-51R from cottonseed. Serological tests indicated that KS-1A contained in the order of 0.05 to 0.1 per cent of protein immunologically similar to CS-51R. A second common antigen, distinguished from CS-51R or KS-1A, was shown to be present in the aqueous extracts of kapok seed and cottonseed. The third common antigen, distinguished from CS-51R and KS-1A and distinguished also from the second water-soluble common antigen, was present in saline extracts and was associated with the globulin-fraction of kapok seed and cottonseed.