A conjugate of hydroxyalkylstarch and a low molecular weight substance, characterized in that the binding interaction between the hydroxyalkylstarch molecule and the low molecular weight substance is based on a covalent bonding which is the result of a coupling reaction (a) between (i) the terminal aldehyde group, or a functional group derived from this aldehyde group by chemical reaction, of the hydroxyalkylstarch molecule and (ii) a functional group, which is able to react with this aldehyde group or functional group derived therefrom of the hydroxyalkylstarch molecule, of the low molecular weight substance, wherein the functional group of the low molecular weight substance is one of the functional groups of a bifunctional linker molecule which has been coupled to the low molecular weight substance or (b) between (i) a functional group derived from the terminal aldehyde group by chemical reaction, of the hydroxyalkylstarch molecule and (ii) a functional group of the low molecular weight substance, which is able to react with this functional group derived from the terminal aldehyde group of the hydroxyalkylstarch molecule, wherein the functional group derived from the terminal aldehyde group of the hydroxyalkylstarch molecule by chemical reaction is one of the functional groups of a bifunctional linker molecule with which the terminal aldehyde group has been reacted, and where the bonding resulting directly in the coupling reaction can be modified where appropriate by a further reaction to give the abovementioned covalent bonding.
