Background:The period course of blood lactate levels could be supportive to evaluate a patient's response to therapy. Serial blood lactate levels in different groups of acutely ill patients. Methods:A total of 200 patients admitted to ICU with critical illness were randomly selected for the study group, Relevant demographic information, clinical history, clinical and laboratory parameters including diagnosis and length of ICU stay were recorded from each patient. The first sample was taken on admission the other samples was taken on 2nd, 3rd and 4th day of admission. Serial arterial sample lactate measurement was done from the patients to note the initial level, time of maximal level and level at time to normal. Result:In the study population 27.5% belonged to the age group of 40-49 years followed by 24% in the age group 50-59 and 20.5% in 60-69 yrs. 57% patients were males and 43% were females. 20.5% patients expired 34.5% patients had hyperlactatemia during ICU stay out of which 31.9% patients expired. Conclusion:Elevated lactate is encountered in a multitude of clinical presentations. Hyperlactatemia is associated with an in-hospital mortality in a heterogeneous ICU population. Patients with elevated lactate levels predicted in hospital mortality and also normalization of lactate within 6 hours is associated with lower mortality. The observation of a better outcome associated with decreasing blood lactate concentrations was consistent throughout the clinical study. Lactate level is an easily measured laboratory parameter which can provide useful information for the bedside clinician when incorporated into the apt clinical milieu.