Rabbits were injected with Drosophila embryo total nonhistone chromosomal (NHC) proteins or with bovine serum albumin, both in 0.1% sodium dodecyl sulfate (SDS). Antibodies were produced which reacted specifically with the protein injected as antigen; the antibodies were not directed against a random denatured protein-SDS complex as shown by failure to cross-react with other proteins in SDS. Antibodies to nonhistone chromosomal proteins were also produced by injecting rabbits with native chromatin. These antibodies reacted with isolated NHC proteins in 0.1% SDS. The presence of low concentrations of SDS did not seem to affect either production of antibodies or their general specificity. The antibodies produced in response to immunization with total NHC proteins or chromatin were directed against at least several proteins as determined by a procedure involving indirect immunofluorescent staining of antibody-antigen complexes in SDS polyacrylamide gels.