Malignant glioma patients were prospectively enrolled into a clinical trial. All the patients were provided with the internationally recommended oncologic standard treatment (neurosurgery, radiation, basic clinical care according to protocol and indication) and randomly divided into a treatment group (receiving complementary immunotherapy with a galactoside-specific lectin from mistletoe, ML-1) and a control group (without additional complementary treatment). Whereas the beneficial effects of ML-1 treatment on immunological rescue and quality of life have been recently shown, evaluation of relapse free/overall survival was performed after a 50 months follow up time. Non-stratified analysis of all the patients revealed non-relevant prolongation of relapse-free intervals/overall survival time for the treatment group. However, analysis of stratified stage III/IV glioma patients demonstrated: 1. a tendency for a prolongation of relapse-free survival for patients of the treatment group (17.43 +/- 8.2 months) vs. the control group (10.45 +/- 3.9 months) 2. a statistically significant (BRESLOW p = 0.035) prolongation of the overall survival for the treatment group (20.05 +/- 3.5 months) as compared to the control group (9.90 +/- 2.1 months). These promising data warrant confirmation in a GCP-based prospectively randomized (multicenter) study, which is currently under consideration.