To help identify the nuclear receptor responsible for ATRA’s effect, BCR-ABL ALL cells were treated with pan-agonists for the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), or RARα, RARβ or RARγ or RXRα specific agonists (Table 1) and the number of viable cells determined by MTT and MTS assays. The gene discussed is RARB; the disease is acute lymphoblastic leukemia.