Retinoic acid receptor (RAR) and vitamin D receptor (VDR) are nuclear receptors that form heterodimers with RXR and regulate the expression of multiple genes. many genes are regulated by both RAR and VDR agonists (e.g. AM850 and 1α,25-dihydroxyvitamin D3, respectively) in multiple cell types. This study examines genes regulated by both AM580 (RARα specific agonist) and 1α,25-dihydroxyvitamin D3 (VDR agonist) in differentiated THP-1 cells focusing on mRNA induction kinetics and additive effects on gene activation.