Purpose: To compare early versus late enhancement in two glioblastoma models characterized by different infiltrative/ edematous patterns. Materials and Methods: Three weeks after inoculation into nude mice of U87MG and U251 cells, T1-weighted images were acquired early (10.5 min), intermediate (21 min) and late (30.5 min) after a bolus injection of Gd-DTPA at 300 μ mol/kg dosage. EARLYTH and LATETH were the corresponding volumes with an enhancement higher than a threshold TH, defined by the mean (μ) and standard deviation (σ) on a contralateral healthy area. ADDTH was the enhancing volume found in LATETH but not in EARLY TH. T2 imaging of both tumors was performed, and T2 mapping of U251. Results: In all tumors, LATETH was significantly higher than EARLYTH for TH ranging from μ+σ to μ+5σ. The ADDTH/EARLYTH ratio was not significantly different when U251 and U87MG tumors were compared. In the U87MG tumors, some enhancement was observed outside the regularly demarcated T2-hyperintense area. In the U251 tumors, irregularly T2 demarcated, a large portion of ADD μ+3σ had normal T2 values. At histology, U251 showed a higher infiltrative pattern than U87MG. Conclusion: In these models, the increase over time in the enhancing volume did not depend on the different infiltrative/edematous patterns and was not closely related with edema.