We have previously shown that the yeast PRP19 protein is a spliceosomal component, but is not tightly associated with small nuclear RNAs. It appears to associate with the spliceosome concomitant with or just after dissociation of the U4 small nuclear RNA during spliceosome assembly. We have found that PRP19 is associated with a protein complex in the splicing extract and that at least one of the associated components is essential for splicing. Taking advantage of the epitope tagging technique, we have isolated the PRP19-associated complex by affinity chromatography. The isolated complex is functional for complementation for the heat-inactivated prp19 mutant extract, and consists of at least seven polypeptides in addition to PRP19. At least three of these can interact directly with the PRP19 protein. We also show that the PRP19 protein itself is in an oligomeric form, which might be a prerequisite for its interaction with these proteins.