[en] The purpose of this study was to investigate the possibility of using [¹¹C]thymidine as a tumor marker for positron emission tomography studies. Biodistribution studies were set up to investigate the in vivo behavior of [¹¹C]thymidine. Simultaneously. the DNA incorporation in fast dividing tissues and catabolism was studied. Our results confirm that [¹¹C]thymidine can be used for detection of cell proliferation of positron emission tomography. As such, it can produce supplementary information in cancer research. (author)