As an extension of our studies on the antitumour properties of various hemocyanins, we sought to compare the antiproliferative effects of hemocyanins derived from two snail species: Helix lucorum (HIH) and Helix aspersa (HaH). This is the first report on the antitumour effects of HaH. We hypothesized that HaH has antitumour effects not only against bladder cancer, as previously shown with other hemocyanins, but also on other cancer cell lines. The antiproliferative properties of the mentioned hemocyanins were investigated in vitro on the following human cell lines: bladder cancer (CAL-29 and T-24), ovarian cancer (FraWü), acute monocytic leukemia (THP-1), prostate cancer (DU-145), glioma cancer (LN-18), and Burkitt's lymphoma (Daudi). The properties of HaH were compared to those of HlH, keyhole limpet hemocyanin (KLH), and two positive controls (doxorubicin and mitomycin C). An antiproliferative effect of the total molecule and one structural subunit of HaH, betac-HaH, against both bladder cancer cell lines, T-24 and CAL-29, was observed. The cytotoxic effect of HaH ranged between 15% and 60% among the other tested cell lines. The endotoxin contamination did not affect the efficacy of HaH. Therefore, HlH and HaH could be appropriate for more detailed investigations of their use as antitumour agents for the studied cancers.