Previous studies indicate neutrophils’ expression of CD14 and CD44 is associated with stage of inflammatory response. This study, undertaken in vitro investigates whether bacterial components affect neutrophils’ CD14 and CD44 expression and lifespan. Neutrophils, obtained through lavage of mammary glands, were incubated with three different concentrations of muramyl dipeptide (MDP) and lipopolysaccharide (LPS). Percentages of apoptotic neutrophils, and of CD14+ and CD44+ neutrophils, were detected after 30, 60, 120 and 300 minutes of incubation. A high concentration of MDP produced a significantly higher percentage of CD14+ after 30 and 120 minutes, compared with LPS and the control, for which percentages remained constant. CD44+ increased at low concentrations of MDP and LPS after 120 minutes, and at 60 minutes for intermediate concentrations. High concentrations resulted in significant increase, this after only 30 minutes for MDP. Analysis of variance indicated incubation time followed by bacterial component, as most important in expression of CD14 and CD44.