Our aim was to examine the hypothesis that vascular smooth-muscle cells (VSMCs) express only ETA mRNA and endothelial cells express only ETB mRNA and to determine which ET mRNA isoforms are expressed in these cell cultures. Using the reverse transcriptase polymerase chain reaction, we were able to detect ETB, ET-1 and splice variant ET-2 mRNA in cultured human umbilical vein endothelial cells (HUVECs) and ETA and splice variant ET-2 mRNA in cultured aortic smooth-muscle cells. The presence of ET-2 mRNA in cultured VSMCs has not been previously reported. These results agree with the hypothesis that ET-1 may be released from vascular endothelial cells to act predominantly on ETA receptors on VSMCs to stimulate contraction of the underlying smooth-muscle cells, and that endothelium-derived relaxing factor release may be mediated predominantly via the ETB receptors on HUVECs. The role of ET-2 expression from HUVECs and VSMCs is less clear.