Introduction: Serum lactate levels are useful indicators of illness severity such as sepsis. Previous investigations have shown that lactate is a potential biomarker for glioma malignancy; mechanism of which may be related to Warburg effect - accelerated lactate production when tumors uniquely undergo aerobic glycolysis. Our study reveals a correlation between serum lactate and meningioma WHO grade. We also observed a relationship between radiation effect on metastatic brain tumors and lactate levels. Methods: Data was collected from the charts of 14 patients with grade I meningiomas, 6 grade II meningiomas, and 9 metastatic brain tumors who underwent resection at our institution from 2013-2014. T test and ANCOVA were carried using R software controlling for base deficit. Results: The mean age was 53 years, with 75% females. There was a statistically significant change in intra- and post-operative lactate during meningioma resections, which had a strong positive correlation with grade (p<0.005). Interestingly, the lactate rise was not significant for metastatic brain tumors (p=0.13), but had a positive correlation with tumors that received pre-operative radiation (p<0.05). Conclusion: Lactate is a potential non-invasive biomarker for brain tumor malignancy, as demonstrated in gliomas and meningiomas. Identifying metabolic biomarkers and their relationship to tumor pathology is important to understanding disease processes and improving patient care.