HIVEN86A is an inducible member of a set of cellular proteins that specifically bind to the kappa B enhancer (Franza et al., 1987; Franza, 1988; Franza, 1990; Ballard et al., 1989; Bohnlein et al., 1988). This enhancer motif has been detected in numerous cellular and viral transcription control domains (Boshart et al., 1985; Sen & Baltimore, 1986; Nabel & Baltimore, 1987). Recently, cDNAs have been cloned (Kieran et al., 1990; Baldwin & Sharp, 1987) that encode the 50 kD DNA binding subunit of murine NF-kappa B (for review: Leonardo & Baltimore, 1989) and the closely related human kappa binding factor (KBF-1) (Kimura et al., 1986; Baldwin & Sharp, 1987). A 350 amino acid domain at the N-terminus of these proteins was found to be homologous with the v-rel oncogene from the avian reticuloendotheliosis virus, strain T (REV-T), as well as a maternal effect gene, dorsal (Kieran et al., 1990; Ghosh et al., 1990). Dorsal is known to activate transcription of certain Drosophila genes (Rushlow et al., 1987). The v-Rel oncoprotein has been identified as a transcriptional activator (Gelinas & Temin, 1988; Hannink & Temin, 1989; Bull et al., 1990) in certain assay systems and shown to be induced by the tumor promoter, phorbol 12-myristate 13-acetate (PMA) in avian cells (for review: Rice & Gilden, 1988). HIVEN86A is also inducible by PMA (Franza et al., 1987; Franza, 1988; Franza, 1990). We now demonstrate that the protein product of the human c-rel proto-oncogene is structurally identical to HIVEN86A.