Using indirect immunofluorescence, nuclear non-histone protein BA was localized in a normal rat liver cell line. Protein BA antibodies immunostained nuclear structures producing a speckled immunofluorescent staining pattern. Nuclear structures stained with protein BA antibodies were sensitive to DNase I digestion, but not to RNase. The speckled pattern of nuclear fluorescence observed with protein BA antibodies was similar to that reported earlier for Sm antibodies, which react with U-snRNPs. Using double-label indirect immunofluorescence, the Sm antigen was shown to be concentrated in the same regions of the nucleus which contain protein BA. Immunoblot analysis of total nuclear proteins with the two antibodies demonstrated that protein BA and the major Sm antigen have similar molecular weights, but are antigenically distinct. In addition, they differ in their extractabilities from the cell nucleus.