We have previously observed that preirradiation with naturally occurring doses of near-infrared (IR) protects normal human dermal fibroblasts from ultraviolet (UV) cytotoxicity in vitro. This effect was observed in temperature-controlled conditions, without heat shock protein (Hsp72-70) induction. Moreover, IR inhibited UVB-induced apoptosis by modulating the Bcl2/Bax balance, pointing to a role of p53. Here, we show for the first time that p53-deficient SaOs cells are not protected from UVB cytotoxicity by IR preirradiation, suggesting that the response to IR is p53-dependent. Thus, we investigated the effect of IR on the p53 signaling pathway. Normal human dermal fibroblasts exposed in vitro to IR accumulated p53 protein, involving p53 stabilization and phosphorylation of serine 15 (Ser15) and Ser20. IR-induced p53 accumulation correlated with increased expression of p21 and GADD45, showing that IR also stimulates p53 transcriptional activity. By modulating UVB-induced targets of the p53 signaling pathway, IR irradiation appears to anticipate the UVB response and to prepare cells to better resist subsequent UV-induced stress. This is reinforced by the fact that IR preirradiation reduces the formation of UVB-induced thymine dimers.