This paper describes the first covalent synthesis of kappa-carrageenan-3'-azido-3'-deoxythymidine (AZT) conjugates. A succinate diester spacer was used to covalently couple AZT onto kappa-carrageenan, resulting in a tripartite prodrug. Two methods (UV and radioactive counting) are described and validated to determine the AZT loading onto the kappa-carrageenan carrier. This polymeric carrier, through its own intrinsic anti-HIV activity, is expected to act not only as a drug delivery agent but also as an anti-HIV agent. Synergism between the two drugs (kappa-carrageenan and AZT) was demonstrated when MT-4 cells were preincubated with the kappa-carrageenan-AZT conjugate prior to HIV-1-infection. A threshold of AZT loaded onto the kappa-carrageenan was required to achieve this synergistic effect. Such kappa-carrageenan-AZT conjugates could be of great therapeutic interest because these conjugates, which contain a low AZT concentration, present improved anti-HIV activities relative to free AZT. Moreover, kappa-carrageenan is a well-tolerated biopolymer, already used in the food industry.