A gene, encoding a liver-enriched transcriptional activator protein (LAP) has been isolated. LAP is a 32-kD protein that stimulates the transcription of chimeric genes containing albumin D-promoter elements both in vivo and in vitro. LAP shares extensive sequence homology (71%) in its DNA-binding and leucine zipper domains with C/EBP. As a consequence, these two proteins show an indistinguishable DNA-binding specificity and readily heterodimerize. In addition, both genes, lap and cebp, are devoid of intervening sequences. Although correctly initiated transcripts from the LAP gene accumulate in the six examined tissues--liver, lung, spleen, kidney, brain, and testis--LAP protein is highly enriched in liver nuclei. Thus, the preferential accumulation of LAP protein in liver appears to be regulated post-transcriptionally.