We investigated the gene expression of 1,25-dihydroxy-vitamin D3 (1,25(OH)2D3) receptors (VDR) and 25-hydroxy-vitamin D3-24-hydroxylase (24-hydroxylase) in opossum kidney (OK) cells. Reverse transcription-polymerase chain reaction demonstrated the presence of VDR gene expression in OK cells. Northern hybridization, using rat VDR cDNA, also demonstrated a 4.4 kbp VDR mRNA expression which was affected by serum but not by 1,25(OH)2D3 and/or parathyroid hormone stimulation. Stimulation with 1,25(OH)2D3 induced 24-hydroxylase mRNA expression which peaked at 6 h. This study clearly demonstrates for the first time the presence of VDR and 24-hydroxylase gene expression in OK cells, suggesting that OK cells are a useful model for investigating the genetic action mechanisms of 1,25(OH)2D3.