The effects of in vitro exposure of beluga whale splenocytes and thymocytes to different concentrations of mercury chloride (HgCl2), cadmium chloride (CdCl2), and lead chloride (PbCl2) were evaluated. The cells were cultured for 66 h with either concanavalin A (Con‐A), phytohemagglutinin‐P, or without mitogen, after which percentage of cell death and proliferation were evaluated. Increased percentage of cell death was observed in Con‐A‐stimulated thymocytes cultured with HgCl2, while the viability of splenocytes was not affected by exposure to metals. Decreased splenocyte and thymocyte proliferation was observed with the highest concentration of HgCl2 and CdCl2 (10−5 M), while lower concentrations of these metals (10−6 and 10−7 M) as well as all the different concentrations of PbCl2 (10−4, 10−5, and 10−6 M) did not significantly influence cell proliferation. Concentrations of metals that were found to affect the proliferation of beluga lymphocytes are similar to those found in the liver of beluga whales from wild populations.