Liver X receptors alpha and beta (LXRα; LXRβ) are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors. LXRs play an important role in the reverse cholesterol transport and govern the expression of many of the proteins that are indispensable for the regulation of normal cholesterol levels in the body. SELEX, an in vitro selection technology, was used on a single stranded DNA library harboring a 12 randomized nucleotide sequence in order to isolate aptamers showing affinity for LXRα. Enzyme-linked assays and surface plasmon resonance measurements showed that the selected aptamers had strong affinities for LXRa with apparent dissociation constants, K(d)s, in nanomolar range. All clones carried CG-repeats, indicating a probability for a similar manner of binding to LXRα. Very high cross-reactivities were observed when testing the aptamers with LXRβ (up to 700%) and RXRα (up to 50%). If instead we regard the aptamer sequences as selected against LXRβ, the cross-reactivities decrease considerably, to 17% for LXRα and 7% for RXRα. Therefore, in the future we are planning to use the obtained aptamers as binders for LXRβ. (C) 2005 Elsevier Inc. All rights reserved.