A new hemocyanin was isolated from the hemolymph of garden snails Helix vulgaris, composed of two isoforms, HvH1 and HvH2 separated on an ion exchange column DEAE-Sepharose 6CL. Structural and immunological properties of Helix vulgaris hemocyanin were studied in comparison with molluscan Hcs Rapana venosa and Megathura crenulata. The possibility of using HvH and RvH as carriers of small molecules (haptens) in immunizing protocols was studied in comparison with KLH, which is a widely used, highly immunogenic carrier protein. By using HvH as a carrier of the well-known hapten TNBS (2,4,6-trinitrobenzene sulfonic acid), an increasing with time production of hapten-specific TFN-gamma was detected in splenocyte cultures of mice, which lasted longer than in case of KLH and RvH carriers. Also, use of HvH or RvH as a carrier of the hapten ProT alpha[101-109] (i.e., the synthetic C-terminal fragment of the poorly immunogenic protein prothymosin alpha) showed that antisera of higher titres than that of the control conjugate (ProT alpha[101-109]-KLH) were obtained immediately after the second bleeding. HvH and RvH may prove to be useful for the development of new antiviral, antibacterial and antitumor vaccines, since they seem to launch strong and specific immune response against the conjugated antigens.