Monoclonal antibodies have previously been raised against chromosomal proteins of Drosophila. Using a biochemical fractionation method for the isolation of large hnRNA-containing structures (hnRNP) of Drosophila tissue culture cells, we show that seven of these antibodies recognize different antigens, and that these antigens are associated with RNA. Analysis of the sedimentation behavior of antigen-containing structures in sucrose gradients reveals that the antigens are differentially distributed with respect both to one another and to pulse-labeled RNA. We demonstrate that the antigens are minor components of hnRNP and are different from the major Drosophila hnRNP packaging proteins, which we have also identified. The antigens are probably involved in the processing of hnRNA in the nucleus.