Abstract: Tumor-active or tumor-diagnostic substances having preferred accumulation in the tumor, which are characterized in that they haveat least two phenolic hydroxyl and/or amino groups,at least one aliphatic amino group, orat least one phenolic hydroxyl and/or amino group andat least one aliphatic amino groupand that these groups are substituted with polyethylene glycol chains whose polymerization degree n is 5 to 250 and whose terminal hydroxyl group is substituted by C.sub.1 -C.sub.12 alkyl ester or ether, each of the substances being substituted by at least two such polyethylene glycol chains.