We showed that UVB enhances the antiproliferative activity of both tryptophan metabolites KYN and KYNA in melanoma A375, SK-MEL-3 and RPMI-7951 cells, which may be related to the increased protein level of p21 Waf1/Cip1 and p27 Kip1 in melanoma cells exposed to UVB. This evidence concerns the gene CDKN1A and melanoma.