The postphagocytic bactericidal activity (PPBA)of buffalo neutrophils for mastitis causing bacteria, namely, Staphylococcus aureus, Streptococcus agalactiae and Escherichia coli, was studied. The percent phagocytosis (PP) and the PPBA were optimum a t 45 and 60 min, respectively, for all three bacteria.The PP was highest for Staph. aureus (88%) followed by E. coli (86%) and Strep. agalactiae (81%). The bacterial resistance toneutrophil bactericidal activity was evident by the absence of PPBA in varying degree, in all of the phagocytically active neutrophils. The neutrophil bactericidal activity was similar for all three bacteria, although, relatively higher for E. coli. This was evident by the total inhibition of PPBA in 31% of neutrophils by E. coli in comparison to an inhibition in 36% of neutrophils by Staph. aureus and Strep. agalactiae.