The effect of ultraviolet B (UVB) irradiation on endothelin-l (ET-1) and ET receptor expression was examined using cultured normal human keratinocytes. Keratinocytes secreted ET-1 in the medium at a level of 2.1 pg/day/10(5) cells. UVB irradiation up to 10 mJ/cm(2) increased ET-I secretion 3-fold, and potentiated expression of mRNA for ET-1. Both ET(A) and ET(B) receptor mRNAs were detected in keratinocytes, and their expression was up-regulated by 5 mJ/cm(2) UVB irradiation.