Figure 4: Day and night variation in reduced glutathione (GSH) content in red blood cells after in vitro treatment with melatonin. The points (□) and (■) represent the effect of melatonin in diurnal and nocturnal blood samples respectively. Dose-dependent variation was observed in both diurnal and nocturnal samples in response to in vitro treatment. Significant change was observed at 10-9 M concentration of melatonin ( ). GSH content is expressed as milligram per millilitre packed RBCs.