1α,25-Dihydroxyvitamin D3 (1,25(OH)2VD3) and retinoic acid (RA) modulate the activation of monocytes (MO) and their differentiation into macrophages (MAC). As these effects are mostly mediated by heterodimers or homodimers of the specific nuclear receptors for 1,25(OH)2VD3 and RA, we investigated the expression of the retinoic acid receptors (RAR) α, β, and γ and the retinoid X-receptor (RXR) α in MO during differentiation into MAC or dendritic cells (DC). The mRNA of all investigated receptors except RARβ was detected in short-term cultured MO. During differentiation of MO to MAC the mRNA expression of the RA receptors decreased. In contrast, along the differentiation pathway of MO to DC, only the mRNA expression of RARγ declined, whereas RARα and RXRα were constantly expressed at a high level. Despite the strong expression of RARα and RXRα at mRNA level in MO-derived DC, the protein expression of the receptors was low in these cells. However, MO and MO-derived MAC showed a strong expression of these receptors at protein level. This suggests that a posttranscriptional or posttranslational mechanism of receptor regulation is occurring in these cells, and in particular in the DC. The inverse regulation of RA receptor expression and protein levels between MAC and DC may control the responsiveness of these cells to 1,25(OH)2VD3 and RA.