Levamisole stimulates proliferation of circulating and intestinal immune cell subsets, gut health and performance in weaned pigs. Can. J. Anim. Sci. 94: 43Á53. With the growing knowledge of the porcine immune system and its endogenous modulation, it has been clearly stated that exogenous modulation through the use of substances able to modulate immune functions represents an important prophylactic/therapeutic approach in prevention/treatment of both stress-and F4 ' and F18 ' enterotoxigenic E. coli (ETEC)-induced infections accompanied weaning. The aim of this study was to evaluate the effectiveness of levamisole (LEVA; 2.5 mg kg (1 BW in 10 mL) applied per os to weaned pigs in proliferation of circulating and intestinal immune cell subsets throughout a period of 5 wk. Changes in proportion or number of peripheral blood and ileal mucosal leukocytes tested were studied either weekly by flow cytometry or at the end of the experiment (day 35) by immunohistology/histomorphometry, respectively. Pigs treated with LEVA had increased proportions of peripheral blood CD45 ' lymphoid cells, CD4 ' and CD8 ' T cells, and CD21 ' B cells (PB0.01) between days 14 and 35 following the treatment. Also, LEVA stimulated the proliferation of CD45RA ' naı¨ve lymphoid cells in interfollicular (PB0.001) and follicular areas (PB0.05) of ileal Peyer's patches at day 35 of the experiment. These pigs had a significantly higher (PB0.05) average body weight (19.7 vs. 17.1 kg) and weight gain at the end of experiment compared with the control pigs (for 15%). We conclude that LEVA stimulated the proliferation of circulating and intestinal lymphoid cell subsets tested and improved performance in weaned pigs, and thus, the drug may nonspecifically enhance their immunity/resistance to F4 ' and F18 ' ETEC strains.