Toward our goal of evaluating 2-HG as a monitoring biomarker for IDH-mutant gliomas, CSF was collected prior to and after resection in six patients with IDH1 mutations determined via immunostaining for IDH1-R132H (n = 5 via Ommaya reservoir and n = 1 via external ventricular drain), all of whom underwent near gross total resections (>95% of tumor volume). The gene discussed is IDH1; the disease is central nervous system cancer.