In this study, we have focused on the preclinical evaluation of 68Ga-labeled peptides (DOTA-c(RGDfK), NODAGA-c(RGDyK), NODAGA-c(RGDyK)2, and DOTA-substance P) and comparison of their in vivo behavior with two clinically established 18F-based tumor radiotracers (18F-FDG and 18F-FLT) in a mouse xenograft model of human glioblastoma. Here, TAC1 is linked to glioblastoma.