Delivering messenger RNA (mRNA) is a new approach for rapid expression and secretion of proteins in human cells. It is providing a more effective alternative to plasmid DNA based expression systems since it may not be necessary to target the mRNA to the nucleus; simply delivering the mRNA to cytoplasm might be sufficient for robust expression. Transfection reagents are actively developed for this application. Developing effective transfection regions for delivering mRNA to endothelial cells is attractive since these cells line up the blood vessels and it is the first cell type that comes in contact with agents administered in the body. The cells also control a plethora of physiological activities in the body, so that they constitute an important cell type for scientific investigations and therapeutic purposes. Below is a summary of recent experience with the use of RJH reagents for modification of human endothelial cells with mRNA.