Inconsistent engraftment of luciferase-expressing tumors, especially GL261 Red-FLuc, has been reported in the recent literature. However, techniques to improve tumor take have not been described. Our study aimed to optimize two luciferase-expressing mouse glioblastoma models, GL261 Red-FLuc and TRP-mCherry-FLuc, which revealed differences in tumor development and characteristics. Congratulations Louis!