Device-related bacterial infections are a significant deterrent to the long-term implantation of the total artificial heart (TAH). Device-related infections in the calf are caused by the same spectrum of organisms, over approximately the same time course, as those reported in man. We studied immunologic function in two groups of 3-4 month old, Holstein steer calves; four animals underwent cardiopulmonary bypass (CPB) only and seven calves underwent CPB and TAH implantation. There was a transient rise in total white blood cell counts and a transient fall in the hematocrit following the procedures in each group. Absolute numbers of neutrophils in the TAH group declined to near or below preoperative levels by the end of the 1 month study period. There was a transient increase in chemotactic response of isolated neutrophils to bovine C5a immediately following CPB and increased hydrogen peroxide production on postoperative day 3. Hydrogen peroxide levels were elevated in the TAH animals from postoperative day 14 to the end of the study period. Serum immunoglobulin levels of IgG, IgM, and IgA did not change significantly during the study period in the TAH group. IgG levels were elevated after week 3 in the CPB group.