As an extension of the previous finding that radioactivity of 14C-labeled D-amino acids after injection is localized preferentially in the tumor and the pancreas of tumor-bearing animals as compared with the corresponding L-amino acids tested, the results of similar uptake experiments using other tumors araa reported here. The present studies show high radioactivity uptake by human colon cancer, human thyroid cancer, and human leiomyosarcoma transplanted into nude mice, and by solid leukemia L1210 and solid sarcoma 180, but not by Morris hepatoma 7316A or 3'-methyl-4-(dimethylamino)azobenzene-induced rat hepatoma. The results suggest the potential utility of 11C-labeled D-amino acids for the detection of some cancers.