Neutrophil and monocyte differentiation can be induced in HL60 leukaemia cells by all-trans-retinoic acid (ATRA) and 1alpha,25-dihydroxyvitamin D3 (D3), respectively, whose differentiating effects can be enhanced by exposure to 'anti-inflammatory agents' and steroids. We have provided evidence that this potentiation is via inhibition of the activity of an enzyme of the aldoketoreductase (AKR) family, but had failed to identify expression of known AKRs in HL60 cells. In this study, we have identified a previously unclassified aldoketoreductase family member (termed HAKR e) that is expressed in HL60 cells. HAKR e is dramatically and transiently up-regulated in HL60 cells within 24 h of exposure to ATRA, further supporting the proposition that a member(s) of this family of enzymes play(s) a role in controlling cell growth and/or differentiation.