The purpose of this study was to detect the effect of nitric oxide (NO) on neuromuscular transmission when stimulated by direct and indirect stimulation at both low (0.5Hz) and High (100Hz) frequency and to study the relation between hemoglobin and NO regarding its effect on neuromuscular transmission.Rat diaphragm preparation was used to study these effects, by measuring the contractile properties Amplitude of maximum contraction (AMC) (ΔY), contraction time (ΔX) and half relaxation time (½ Rt) for the different groups; The groups included: (a) low frequency group exposed to low and high frequency electrical stimulation and (b) high frequency group exposed to both low and high frequency stimulation.There were significant changes in the contractile properties of different groups.On the basis of these finding, it is suggested that NO has dual action on neuromuscular transmission facilitatory at pre-synaptic level and inhibitory at post synaptic level and that hemoglobin acts as scavenger for NO.