Cephalosporanic acids (CEPHAs) such as dihydro-1,4-thiazine derivatives and 2-hydroxyalkyl-1,3-thiazolidine-4-carboxylic-acids, (HOTCAs) are both important biologically active molecules and complexing agents for several metals such as Fe, Zn, Pb, etc. The simplest way for the study of the effect of complex formation upon the biochemistry of these compounds requires radiolabeled complexes. As99mTc radioisotope gives the best opportunity for imaging the in vivo process,99mTc-CEPHAs and HOTCAs were prepared and investigated. It was found that biologically active molecules like CEPHAs and HOTCAs can be labeled with99mTc with good radiochemical yields. In case of one CEPHA compound, low but definite myocardial uptake was observed, while 3 of the HOTCAs showed characteristic renal uptake and wash-out without visualization of any other organs than the urinary tract.