Isoform-2 nitric oxide synthase (NOS-2) mRNA expression and nitric oxide (NO) production are induced in endothelial cells and monocytes by cytokines such as gammaIFN and LPS. We evaluated NOS-2 and isoform-3 NOS (NOS-3) mRNA expression and NO production in human monocytes and human umbilical vein endothelial cells (HUVEC), under basal conditions and after incubation with physiologic concentrations of vasoactive hormones. NOS mRNA expression was detected by reverse transcription polymerase chain reaction (RT-PCR) and NO production by electronic paramagnetic resonance spectroscopy (EPR). We showed that NOS-2 mRNA expression and NO production were induced by stimulation with epinephrine, dopamine, endothelin-1, and angiotensin II, both in monocytes and HUVEC. NOS-3 mRNA expression and NO production were detected under basal conditions in monocytes and HUVEC and were not modified by the presence of vasoactive hormones. Human endothelial cells and monocytes express the NOS-2 and NOS-3 mRNA and the inducible NOS-2 mRNA expression increases after vasoactive hormone stimulation.