The effects of in vitro exposure of beluga whale splenocytes and thymocytes to different concentrations of mercury chloride (HgCl₂), cadmium chloride (CdC1₂ and lead chloride (PbCl₂) were evaluated. The cells were cultured for 66 hours with either concanavalin A (Con-A), phytohemagglutinin (PHA), or without mitogen, after which percentage of cell death and proliferation were evaluated. Increased percentage of dead cells was observed in Con-A-stimulated thymocytes cultures with HgCl₂, while the viability of splenocytes was not affected by exposure to metals. Decreased sp] endocyte 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^-7M) as well as all the different concentrations of PbC1₂ (10^-4, 10^-5 and 10^-6 M) did not influence significantly cell proliferation. Methyl-mercury affected cell proliferation at concentrations 10 times lower than mercury chloride. 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.