Abstract: The invention relates to conjugates composed ofa) at least one polyalcohol or a derivatized polyalcohol,b) at least one active agent,c) at least one linker andd) a protein,wherein the polyalcohol(s) or the derivatized polyalcohol(s) are polyalcohols or derivatized polyalcohols which are not recognized by the defense system of an organism as exogenous, and the protein is a protein which can be taken up by the tumor specifically or non-specifically, and is not recognized by the defense system of an organism as exogenous. These conjugates are suitable for, on the one hand, making possible a very sensitive method in nuclear medicine for the diagnosis of tumors and, on the other hand, for example also offering new methods for diagnosing tumors in X-ray diagnosis, computerized tomography, nuclear spin tomography, electron spin resonance spectroscopy or electron microscopy.