The significant changes in morphology and nitric oxide synthase (NOS) activity in cultured human aortic endothelial cells (HAEC) were observed when these cells were exposed to LPS, IL-1? and IFN-?. NOS activity increased at 6h of treatment, the time point that HAEC began to change and elongate. The cell shape became fibroblast like and the length to width ratio of the cells increased 2 times of that of the control at 20h treatment, the time point that NOS activity returned to control level.