The effect of exogenous nitric oxide (NO) on growth, viability and ultra-structural of B. hominis was assessed in vitro by sodium nitrite (NaNO2) in 0.6 mM, 0.8 mM & 1 mM concentrations. The viability of B. hominis was identified using neutral red stain. The role of NO as an endogenous oxidant was assessed by identifying its level in cecum tissue, ileum tissue, blood and stool elutes of mice infected with B. hominis symptomatic human isolates using reactive nitrogen assay compared to control. In vitro study revealed that NaNO2 inhibited the growth and decreased viability of B. hominis with minimal lethal concentra-tion dose 1 mM on the 4th day while, minimal effects were detected with 0.6 and 0.8 mM. Transmission electron microscopy study proved that apoptotic-like features were observed in growing axenic culture of B. hominis upon exposure to NaNO2. These changes were not only found on the vacuolar (central body) form but also they were detected on granular, multi-vacuolar and cyst forms. In vivo study proved that high levels of NO were found in infected mice compared to low changes in control group. The high levels were in cecum tissue particularly. The mean levels of NO among infected mice were 211.8 +/- 20.7 microM in cecum, 90.4 +/- 11.6 microM in ileum, 60.1 +/- 4.7 microM in blood and 63.6 +/- 7.3 microM in stool elutes while, the mean levels of NO in control mice were 70.2 +/- 3.1 in cecum, 67.8 +/- 4.7 microM in ileum, 30.9 +/- 4.2 microM in blood and 28.1 +/- 2.9 microM in stool elutes. The differences were statistically highly significant. NO-donor drugs proved useful in treatment and increase the host resistance to B. hominis.