The applicability of five different rodent tumors for experimental PET has been investigated. L-[1-11C]Tyrosine was a better indicator for the growth activity of the tumors than [18F]FDG. For experimental PET, the three mice models studied appeared inappropriate; the Lewis lung tumor and the fibrosarcomateous FIO 26 had too low a tyrosine utilization, while the lymphosarcomateous LY showed insufficient tumor-to-background ratios. Of the two rat models, the necrotic Walker 256 carcinosarcoma was less suitable. By using L-[1-11C]tyrosine, the solid, rhabdomyosarcoma tumor offers good possibilities of monitoring therapeutic interventions with PET.